I'm sure it used to be that the sin bin was only used for technical offences, such as persistent offside, professional fouls and so on, whereas the red card was used for dangerous foul play.

Maybe a return to that would help clarify when the use of the sin bin is appropriate. "On report", in my opinion anyway, should only be used for mass incidents involving several players - in other words, the incident should be on report, rather than the player himself, meaning that anyone involved could potentially be cited.

Report should be used when somethings happened that the Ref hasn't seen and therefore can't accurately judge.
Sin bin should be used for players following a dust up and the technical offences you state.

There's been a few instances this season of the fullback holding down layers after a break and not getting penalised, never mind sin binned. This is when I'd like to see it back.

A damn site more than you

Tripping was an automatic--and that is the key word--sending off offence even if it was a reaction thing, i.e.getting caught wrong footed rather than malicious, but that was changed many many years ago.

FWIW I believe that the old rule should be brought back and ALL trips should merit a red card but that aint the rule now.

I don't get all these people saying the officials all missed the trip. How can it have been put on report and penalised if it wasn't seen?

In my playing career, I've seen a 2 broken legs from people "reacting" and sticking their leg out. I always assumed that was why they were treated so harshly.