I upvote many posts for many reasons. I bookmark only a few posts because I find them important to me for a specific reason and I will be wanting to get back to that content at some time in the future. Similar to how I book mark a webpage in my browser. I don't bookmark for posterity but rather for utility.
yes, i understand that the ideal situation ut if you want to save many post in the long time will need some kind of searching system
and notification to the author was ok with favs but no sense with bookmarks