If you're talking about laying the keyboard on your lap while you play: I was getting a seriously painful keyboard wrist, I tried laying the keyboard on my lap and it fixed the problem.
That type of layout makes your shoulders to be at different height which is not good in case you play many games regularly, and that's why cooller plays now with keyboard on table. Placing hand with elbow (not wrist only) on the table is considered by some players giving more stability and less stress for wrist. In terms of aim and movement - no advantages, just a matter of habit and personal comfort preferences.
For me a modification of that style is more comfortable than office posture. I like to rest my feet on the table because my feet has shitty bloodflow so I play with mouse on the table, keyboard on my lap and feet resting on the table or my stereo ampliifer.