As long as there've been MCU movies, there have been post-credits scenes. Along with Stan Lee cameos, Easter Eggs and humour used even at the darkest times, they're among the pillars of this universe.
With a number of functions - introducing characters, killing them off, adding extra jokes or teasing future storylines - there's a broad spectrum across the more than a decade of films we've seen so far. But not all of them have been equally great.
Still, no matter how lightweight the joke, you should never, ever leave the cinema early, because you can never quite tell when you're going to get a huge cameo or a look at what direction Marvel is going in next. And they definitely know the hold they have on us...
37. Ant-Man - Bucky
Like the Doctor Strange and The Avengers mid-credits scenes, Ant-Man's post-credits scene is just the reuse of some footage from another film - in this case Civil War - and is intended as a sort of Ant-Man Will Return reminder for that movie.
The problem with it is that it references things we have no idea about, offers no context and generally makes no sense at all as a stand-alone scene. A better scene could have been chosen to suit the purpose of teasing Ant-Man's involvement, which is somewhat frustrating too.