It is possible to train the human body into needing much less sleep. It is sleep quality and not amount that counts.
I have heard about people from military elite educations, who make their body used to no more than 4 hours of sleep at night. And they are still fit and surprisingly energized the next day ready to continue their rough training.
First of all it all depends on ones own body. Some need more, some need less sleep to reach the same level of rest.
Then it also depends on your sleep quality. You've got to fall a sleep fast and immediately go to the deep and good sleep, and get quickly past the REM sleep (Rapid eye movement sleep) which is the more superficial dream sleep.
Then your body also has to be able to recover fast. This follows your psysical condition level.
Lastly, remember to eat healthy and have the right amounts of protein etc. after training for the body to have perfect conditions for recovering fast.
If your body ever shows signs on burnout you should react. This could be simply having sore muscles the day after the exercise, if you do this exercise of these muscle groups regularly but with no soreness. If you find yourself loosing focus and concentration and feeling tired then of course you need sleep.
In the end, without training to need less sleep, some people just appears to need less anyway without any effort. It varies from approx. 7-9 hours in average. If you are the 6-hours kind of guy this could be just you, and you should find out by about this. Give it ago and keep focus on soreness and pain in the very early stages.