Problem: One of the main reasons I visit my flagging history is to look for helpful flags on answers that are not deleted. Flags can be marked as helpful without the post going away when a well-meaning reviewer edits a post while it's in the Low Quality Posts Queue, when the author edits the post, or when the author deletes and undeletes the post. In many instances, the post has not really been improved and should still be removed from the site, but now all flags and delete votes are removed. When I identify such posts through my flagging history page, I bring them to the attention of the community either through a chat room or by re-flagging.
Unfortunately, the flagging history does not make it very easy to find helpful flags on non-deleted posts. Basically you need to scan the list of flags looking for links with the white background indicating a non-deleted post:
instead of links with the gray background indicating a deleted post:
and then you need to ignore nearly all of the links with white backgrounds because they are helpful comment flags on posts that have not been deleted (this proposal could help reduce the visual clutter). Compounded with the relatively small number of flags listed on each page (meaning recent flags often scroll off the first page before they're handled), the current user interface makes it quite challenging to identify helpful flags on non-deleted posts.
Proposal: I propose an option to filter your flagging history to helpful flags on posts that are not currently deleted, either using tabs at the top of the page or a check box. Given that the flagging history page current displays both whether or not a flag was helpful and whether or not the relevant post is deleted, I would hope this would not be a heavy-duty implementation effort.
Similar Proposals: Filtering by each category of flag shown on the right side of the flagged posts has been proposed here and here and here and here and here. While I think this would also be a fabulous feature (the other main reason I come to the flagging history is to check out declined and disputed flags), the current proposal differs in requesting a subset of the helpful flags on posts instead of all of them.