Ive spent most my adult life living off 3-5 hours a night. Until I started lifting, then I enter an immortal struggle to get 7 (8 makes me groggy). I always just miss a good cut off point, then have to wake up in a few hours. Though recently for a couple months I been getting 8-10
It is very important, but it does depend on your body. Look at marine training. 4 hours of sleep in 84 hours
my bro just did that kinda deal.
But lacking in sleep does slow muscle recovery, increases chances of injury, and usually just makes you feel pooey. I would also say add in another meal to your day on a 4 hour nap night. Since this is in the bulking thread anyways, I dont think that would pose an issue. When I have less sleep I find fruits and some nice carbs really refresh my mind. Recommendation is 7-9 depending on person. It does effect muscle growth.