I don't think I ever need even ten, but I inevitably end up with 30+ spread across two browsers because I just don't close. Then I close all in CTRL+W rage* and rely on history + memory to find anything I'd like to return to.

*Thanks for your post. It reminded me to go into firefox and unset "Open previous windows and tabs," which I accidentally turned on and has ruined my ability to rage X out of firefox everytime I have too many tabs.