> For instance, almost every website has a thing where if you enter in a wrong username OR wrong password it’ll tell you that you got one wrong, but not tell you which one. This is good for security because you can’t use the information to figure out usernames, but it is a GIANT pain in the ass for people like me who can’t remember which username they registered under. So if you don’t actually care about exposing usernames (maybe on something like a forum or Pinterest where they’re public anyway), consider revealing the information to make it more convenient for users.
YES! Such a pain in the arse for a tiny theoretical unimportant security benefit. In some situations it is warranted, e.g. dating sites. For something like Amazon or Wikipedia who cares if you know that I've registered there?