TTTE/RWS Wrecks: What makes a good wreck?

Okay, so we all know that most of the stories and Season 1-4/18-present are at least grounded in some reality and have certain elements that could have or did happen in real life (the slip coaches, for example, were based in reality, as was James and the bootlace incident, Godred's wreck, etc).

On this last note, what makes a good or bad wreck? Discuss below.

I think a good wreck is a wreck that is realistic (so it can happen to steam trains). I also think a good wreck has some explanation for being there, and is not just there for the story.

I also think that a good wreck, or incident should be varied, as in why, and what happened.

These are some of my thoughts, but, I honestly don't know much about this sort of thing.

I good wreck is when there's a big crash.

Yup, that and nothing more for me.

A good crash is exciting, but must have some realism. Sometimes, a very exciting but not very realistic crash (Thomas in the cavern - SLOTLT) or vice-versa can be good, but the best crashes are both, like James' crash in TAB, the prime exams of a great crash. If you ask me, I'd like to see some mild crashes nowadays, like something you'd see in the RWS or Classic Series. Something like a small derailment. Things like Rock 'n' Roll, Off the Rails, Toby's Tightrope, or Steamroller. But don't stop the crazy crashes!

No smoke or dust to block it.