The value of writing comments intended for your future self was confirmed in a strange way for me: I once found myself googling some faintly obscure question of systems programming, and soon found an article that answered my question perfectly.  At that point I noticed with considerable surprise that I was reading a web archive of a Usenet posting I had made myself, some 10 years prior - of all the people to randomly run into on the Internet, your past self is one of the strangest.