Attention MMM... A very short cliff note follows:
The CNS has the affect of governing the majority of muscle nerve functions (including those satellite cell message units). In referring to maintenance, recovery/repair/advancement and general body health. The CNS will need (as the mean average) 72 hours (some disagreement on that) to return to a somewhat normal state after a hard workout. That normal state will allow the muscle fibers/cells to have the opportunity/time to heal and grow a little larger than before that workout (in theory anyway). And be ready to adapt to the next demanding workout. To say the the CNS is one of the most important factors in steady gains, including slow or no gains, would be an understatement.
Some say a complete return to a normal state for the body may require 2 to 3 weeks, as some sports medicine people suggest, though that may be to the extreme. To function at near 100% the CNS has to return to at least that, or near that. Mike Mentzer (Art Jones ,though they may differ slightly) seemed to had been of this opinion of having workouts few and far between in his training protocol. After his Black Flag training day, you would need all the extra rest you could get before the next battle with the weights.
There is another important element that also uses the letters CNS, that may need quick attention. It is "Candidizzle Needs Study". Now he seems like a nice enough chap, though tending to be a mite arrogant and self absorbed. I am sure as he matures in life and learns to respect and listen to the experiences of others, in the lifting game or anything else, he can improve himself greatly. Both with knowledge and a physically superior body. Knowledge is a liftime pursuit but you can get impressive muscle mass in not that many years, if you know what you are doing. Not talking about drugs here. Good Luck.