I’m taking this one part out of context because I find that my use of favourites confuses people. I don’t repost things very often - maybe once every two or three days - but I mark up to a dozen things as favourites every day. Now that I can more or less trust Twitter to report them, their previous function as a bookmark to myself has been joined by those of being a nod to the poster, as well as a little recommendation to those who take the time to look (either at the activity page, a site like Stellar, or via the API).
In other words, Twitter’s favourites have become as worthwhile as Flickr’s, which have served the same purposes for a while now.
(I have a huge draft on favourites from last summer which needs splitting into pieces. Eventually.)