This site is a treasure full of information and often it is scattered around the whole site which makes it unnecessarily difficult to find a post which contains sought information. You can watch threads, but that is not good enough. The bookmarks add-on allows you to save and tag single posts so you can always find interesting content without searching for it. This would be an incredible enhancement to this support forum and that's why I suggest to install it here.
I know it can be misleading for new users if they see a feature here that is missing in their fresh xenforo installation, but you always can enable this feature as an user option with the note that this is not a default xenforo feature (or put this in core).