In my humble opinion every animal consistent of multiple cells alive on this planet developed sleep for just one reason: the very same reason plants sleep. Our planet has a night phase and without sun little energy is left. So as a consequence the best one can do is to clean up internal processes or go into some sort of energy saving mode. Ofc this is heretic to some individuals...
The above mentioned study links raising HDAC2 to reverse effects of Alzheimer's disease.
I doubt that the autism study with mice really 'cured' autism. I think the cancer drug reduced cognitive abilities, so mice seemed to react 'normal'.