An article today says "brain waste is cleared most effectively when sleeping on one's side," so people who sleep that way have less trash in their brain and are less prone to Alzheimer's, Parkinson's and other brain diseases. I'm not so sure about that. I sleep on my side, but I have Parkinson's and, according to my wife, my brain is full of all sorts of trash.
On a related note, my since she retired my wife is on a house organizing spree. She's doing a very nice job, and I'm loving the results, until she told me that she is "throwing out everything that's old and worn out." I found that statement rather alarming until she assured me that no, that did not include me.
Interestingly, she did not claim that I am not old and worn out, merely that she is not throwing me out.