Sleep, it is oh so very, very important! Sleep is when your body grows, when you produce growth hormone (which is in short supply the older you get), when your body regenerates after all of the stress of the day.
The growth you experience from weight training happens outside the gym, after you have eaten proper nutrients, and then sleep. Take away one or the other, or short change yourself and your efforts are wasted.
You can train like a champ, but if you do not allow your body enough sleep, it will not grow or improve, simple as that.
You cannot "catch up" on sleep. Sure, you can sleep in and rest longer on weekends if you want or feel you need to, but you cannot stay up late and then plan to sleep in to make up for that lost sleep, it doesn't work.
People who stay up later on weekends, and sleep in are not as successful in the gym as those who adhere to a "regular" schedule. The body is a finely tuned machine, that runs on a schedule, mess up the schedule and it rebels!
Often, you may find that you end up skipping your training too- you stayed up late, slept in, had things you had to get done, so the gym time suffered.
You should try to limit TV, computer, all electronic and light stimuli before bed. Give your brain time to relax and unwind.
Many people confuse lack of sleep with "over training". They are pushing themselves to the limit in the gym, eating right, working a full time job and are exhausted. They get sick a lot too, their immune system is shot and they blame it on "over training".
Well, I hate to burst your bubble, but hardly any of us, in most cases, unless you are an Olympic level athlete are "over training". What is happening is "under sleeping". You have "sleep debt".
People who have a mid afternoon slump can usually blame that on sleep debt too, their body just didn't get enough.
You try to fit it all in, and then you still want to watch four hours of TV at night, or go out with friends after work, so you end up going to sleep later than you should. Cut out the TV and the partying go to sleep earlier instead and you will suddenly feel better, you will not feel "over trained" and you will probably have better results.
You will know you are getting enough sleep when you start to wake at approximately the same time every single day, regardless of when the alarm sounds. So, if you usually get up at 5:00 am, and then on the days you aren't working, you start to automatically wake at that same time, you are getting enough sleep.
Here is a saying from Al Schoterman, a Strength Coach and Olympian regarding the importance of sleep and rest for the athlete.
The Phases of Rest
Never run when you can walk
Never walk when you can get a ride
Never stand when you can sit
Never sit when you can lie down
Never lie down when you can go to sleep
` Al Schoterman