First of all, before starting explaining everything, we have to list all the different kind of sensitivities:

- from 0.5cm to 5cm = ultra high sens
- from 6cm to 9cm = very high sens
- from 10cm to 15cm = high sens
- from 16cm to 25cm = medium sens
- from 26cm to 35cm = low sens
- from 36cm to 45cm = very low sens
- from 46cm to anything slower = ultra low sens

Then we have to list the different dpi steps to use according to each type of sensitivities:

- ultra high sens = 3000dpi and above
- very high sens = from 2000dpi to 3000dpi
- high sens = from 1200dpi to 1800dpi
- medium sens = from 800dpi to 1000dpi
- low sens = from 400dpi to 500dpi
- very low sens = 400dpi
- ultra low sens = 400dpi and lower

And finally we can start about why I made this thread:

Comparing low sensitivity at 400dpi -VS- high sensitivity at 1600dpi; 26cm and low dpi -VS- 13cm and high dpi.

I'm currently using a Zowie by benQ ZA11 at 1600dpi 1000hz and 13cm/360°. For testing low sensitivity I used obviously the same mouse but at 400dpi (and then set it to 26cm/360°).
One thing I have to mention is that high or low dpi steps, the feeling, the responsivness of the mouse is basically the same, might not be the case on some other mice (depending on sensor(s) and native dpi step(s)).
I have to mention also, that, over the years, I tried basically all kind of mice, from Razer Krait with angle-snapping to Steelseries kinzu v1 with hardware accel to abyssus 1st edition with no acceleration nor angle-snapping etc, to some other Zowie, Razer and Logitech mice. Also tried many different dpi steps on all kind of mice, from 400dpi to 3500dpi.

Ok, so, basically I played 2 or 3 days for like 3 hours/day on 400dpi 26cm, coming from 1600dpi and 13cm.

Now let's list the pros and cons of low sens compared to high sens:

+ at long range, railing is stable and when you do the "wait for the enemy to come into your crosshair", you rarely miss a shot due to the stability of the sens
+ at long range, flick rails are ultra precise, as long as the opponent doesn't do too large movements (but if he does you rather use strafe-keys and wait for him to come into your crosshair)
+ med to long range LG'ing is very stable and feels good, as long as the opponent doesn't do too large strafes (in which case you might get fucked up, or just try to "mirror strafe-aim" his movement pattern)
+ med to long range RL shots are effortless
+ shakyness is almost non present, your aim is almost very stable all the time
+ if you're young, and got a lot of adrenaline inside you (:D), you might like the fact that you have to basically do table tennis on your mousepad (:D)
+ sharp & solid aim in a 10° to 80° angle

- some quicker flick rails are almost undoable
- some larger flick rails requiere much more effort to be done properly
- obviously you have much more trouble, or at least need to put much more effort, against med-to-long strafes, especially if they are spammed
- RL at close range is awful, so you have to rely on your positioning and movements more in order to not get tricked by the opponent's dodges
- fast mid-air at close range forces you (again) to make more effort if you want to hit them
- if the opponents leaves your screen, or in other words leaves the 10° to 80° angle, you react much slower and there again have to put much more effort to make an accurate flick shot
- LG at close range makes you more dependent on your movement pattern, countering someone "circle'ing" you is harder and you have to use the right movement pattern in order to compensate that
- LG at med-long range is harder if the opponent starts to do a mix of med and large strafes or goes in the same direction while doing so
- 180° turns are doable but are done slightly slower and, once again, requiere more effort (because you have to move your arm very quickly on a rather large distance)
- 360° turns are doable but much slower, even if you got very quick arm
- certain rocket-jumps are almost undoable
- strafe-jumping and bunny-hopping become harder if you reach a certain speed because you have to make quicker and larger movements with your whole arm, basically
- after 2 hours straight of playing, your hand and/or arm/forearm starts to lose some of its "power", so basically, if you play more than 4 hours on low sens, you start to play worst and losing stamina
- need more space on your desk / bigger mousepad
- you often end up in "unnatural" mouse position on the mousepad while tracking long strafes
- more effort, slower
- more effort, slower
- more effort, slower... and so on...

Noticed how many times I used the word "effort" ? Why did I do that ? Simply to emphasize the fact that in most situations, you have to put 2x the effort you do compared to when you play on high sens.
Noticed how many times I used the word "slower" ? It's obvious, the wrist is ALWAYS faster than the forearm, and when on high sens, when you have to move your forearm, the distance you have to travel is 2x shorter, means that you can do that 2x faster than on low sens, for the same result.
Actually, hitting very hard is basically possible in any situations with low sens BUT you need more effort and sometimes you just can't, you have to compensate with your movements, which makes you more predictable.

High sens gives you more freedom at the end, open possibilities of more playstyles / movement patterns.
Low sens makes you more predictable, ofc you can still hit hard as fuck with low sens, but if you want to adjust or change something, you often end up forced to use your strafe-keys in order to make it effective.

Also, one last thing, which is very important in my humble opinion. I'm not talking about low sens -VS- very high or ultra high sens. Because anything higher than high sens (1200dpi - 1800dpi 10cm - 15cm) is too extreme. Basically with very or ultra high sens it's the same problem than with very or ultra low sens : you have less freedom, you are basically forced to almost use the same movements/playstyle, and trying to be like ultra-good at it (practice practice practice (c) Fatal1ty), but in this case you become more predictable.
For example, on ultra high sens, it's VERY hard to track short strafes properly, which means that you'll have to force large/long-strafes ALMOST all the time.

People often say that the sweet spot for sensitivity is between 22cm and 30cm, not too high, not too low. Actually, they are wrong, the sweet spot is from 10cm to 15cm (high sens). Because with such a sens, you still have to move your forearm in some situations, you can still track short-strafes if you "calm down" and do small mouse's movements. You can move faster with less effort, do 360° faster, do flick/mini-flick shots snappier (it's just that you don't use your whole forearm in order to do so, at least compared to very low sens and slower), you're not limited to a "10°-80° angle type of aiming", you're FREE :).

The reason why people are using 400dpi and low/very low/ultra low sens is because they just copy/pasted all the CS:GO pros, and some aim monsters at Quake, without trying to find by themselves which setting is worth considering.
Having 45cm+ at CS:GO makes some sense because it's almost always long range fights and the opponents very rarely go out of your "10° to 80° angle" of vision. But in any fast-FPS high sens is the sweet spot. Not too high, just high.