When coming up on a very slow vehicle, or stopped traffic, do you ever think to put your four way flashers on?

To warn others that are coming up behind you?
Yesterday I waited 6 hours behind a bad accident a bus driver rear ended two cars and a farmers tractor killing the farmer, and very seriously injuring six others including himself.
The farmer was moving some equipment down the road to another field.
The last car didn’t have his flashers on to warn others coming up that he was in a slow moving line, not saying that would have prevented the accident but it might have given the bus driver a better chance.
What is your opinion?