My Dropbox story: after I upgraded from Mountain Lion to El Capitan, the sidebar in the Finder went buggy (no way to remove a folder from the sidebar without restarting the Finder). After I started arranging for this next command line to run at the start of every OSX session, the bug went away: `killall -9 garcon`. This garcon identifies itself in Activity Monitor as "Dropbox Finder Integration".
Needless to say, I never asked or gave consent for Dropbox to integrate with the Finder (and sync still seems to continue to work after I disabled it).