I’m not sure how common a practice throwaway games are, but I know I’ve played in one for sure. Sometimes a group is doomed from the start and finding that out before you actually start playing is worth the time put in to make sure. I knew a couple of guys that just hated each other from the second they met for no reason at all. Well, apart from one of them was arrogant and secretly afraid of people finding out he wasn’t as smart as he thought and the other was tactless and prone to constantly correcting others. They could not, would not, get along. So the game ended and was put together without one of them, and one of me but that was unrelated. My understanding is that the game that started after they sorted out that power dynamic is still going on to this day in one form or another.
Every DM is different, every group is different, and anything thing you do with other people is going to fall prey, to one degree or another, to all the things that anything to do with groups of people do. Which is fine, but some people don’t realize that right away. Experienced DMs tend to be the kind of people who are good at deescalating problems and tolerating the constant nonsense associated with other humans. I’ve never met a successful Dm that couldn’t just let stress just wash over them like water over stone. It wore them down like anyone else, but at a much slower rate.