I’d like to able flag or bookmark particular discussions to follow. It would also be nice to receive an email when a flagged discussion receives a new response.
It is possible to flag a discussion to follow after a response. But, there are also discussions that I’d like to follow, even if I haven’t participated in the discussion.
If you click that even on a discussion that you did not participate it will appear in your profile under “Discussions” → “Followed”, which is a sort of bookmarking mechanism:
You will receive email notifications for “Followed” discussions. Also I would recommend not to use term “Flag” for this because it means a different thing and is also available on Community. To “Flag” means to sent private message to moderators about usually a troubled post that needs some attention - via clicking “Flag” button in the lower right corner: