The topbar only tells us about reputation gains (see related issue with lost rep). But sometimes it only half-tells us:

The explanation of that +1 is nowhere to be found here. An answer that I downvoted was deleted (hence the return of my 1 rep), but I'm active on several sites and sometimes it takes days (or weeks or months) for such posts to be deleted, so asking myself "what have I downvoted recently?" doesn't necessarily help.

If we're going to show the notification, shouldn't we also show the explanation?