Sometimes people hold up the dungeon by asking you about why you did something, but that’s only because they’re idiots who think you should play their way instead of the fun way. Sometimes they try to kick you because they’re horrible people who care more about being douchebags than just getting on with the dungeon. But most of the time they’re good players who just play the game like they should and don’t totally freak out when other people take short AFKs.
If you do ever get a group that sucks enough to kick you, don’t worry, just queue again straight away. The next group probably wont hold you back as much as they did. And anyway, Blizzard wont let people kick you too much, because at least they understand how unfair it is to get kicked from groups all the time.