The whole premise of there being a single function or main function of sleep seems slightly far-fetched IMHO. For example, is the brain's function to think rat

The whole premise of there being a single function or main function of sleep seems slightly far-fetched IMHO. For example, is the brain's function to think rationally? To speak and understand language? To unconciously regulate bodily functions? Wouldn't it be more likely that due to the brain's multifunctional nature that an evolutionairly pruned process has developed which encompasses multiple necessary subroutines (energy preservation, memory consolidation, waste cleansing, etc.)