This happens to me once or twice a week... I want to perform some action (such as abandoning a differential) and attach a comment to the action that refers to the relevant discussion (for an example, see D9942#13). Currently, it is a bit of a pain to work out which comment ID I want to refer to.
Before quoting was available, I would literally just manipulate the URL and keep incrementing the ID until I found the comment that I was looking for. It is slightly less painful now (I just quote the relevant comment and copy the `T123#45` identifier). I think it would be nice if hovering over `.phui-timeline-icon` (or whatever) would expose these details.