OK, I have 4 mirrors on my car, all flat mirrors. I have the inside mirror that looks straight back. On both sides, outside, the mirrors point out to view what would otherwise be a blind spot. Why would I have them pointed straight back when the inside mirror does that job? That way I can see all around the car. This has saved my @$$ several times and I don't have to move my head to look for cars in the blind spots. I do this on my modern cars too.
Oh, and the 4th mirror. That is on the driver's side and looks down at my back fender. I use that as a backup aid when backing into my garage and when backing into parking spots. I like to back into parking spots because it is safer when I go to leave because I have a good view of traffic passing in front of my car. My modern pickup tilts the mirrors down automatically when I back up.
I don't like the convex mirrors because it is hard to judge how far away the car in the mirror is.