[tdaltonc]

In addition to the chemical ones others discussed, there is informational "garbage collection" as well. There are a bunch of motor tasks that only show certain types improvement after sleep - not time, sleep. There are also rodent studies where you can do a learning task and then "clear" part of their hippocampus using optogenetics. If you clear it before sleep, they forget what they "learned" if you clear it after sleep they still remember it. Again, multiple clever conditions to control for time and separate it from sleep.