Here is a particular use case:
I've started to use the favourites, as suggested by this comment, to save questions/posts as a reminder that they need editing:
On the smaller sites you should rate limit yourself to, say, 1 per day. This requires some organisation, but the 'favorites' feature can be used for that.
"Why?", I hear you ask. Because, on any particular day, I've have probably already edited a number of questions and I don't want to flood the Active question list with my modified questions. So, I have been saving them up for a rainy day.
Today is such a day, and so, for the first time, when I opened the favourites list and sorted by added, I have just realised that I can't see when I added them, only the date of the last modification.
Would it be possible to show the added date, as it would help me remember why I favourited a particular question. It is a shame that I can't make a private online note1, when I favourite a question, as to why I am favouriting it, so having a date added displayed would be the next best thing.
I feel that this is different from Can the date a question was added as favourite be shown on the favourites list on the user profile? as I am asking for the date to be shown only when sorting on the added tab.
1 This may become a future feature-request of mine.