green1, how long have you been driving? Nothing wrong with checking over your shoulder but setting mirrors properly is counterintuitive. (If the object in your side view mirror is your own car it is set too close).
Checking over your shoulder is mandatory. Both for safety, and by law in most jurisdictions.
There is no possible way to set your mirrors that does not involve a blind spot.
The mirrors don't suddenly get larger if you angle them a different place. And if you can't see the side of your car you really have no clue where you are seeing. It's dangerous. The side of your car should take up none of the space in your mirror, just a mere sliver on the edge, just enough that you know where you are looking, and to prove there's nothing along the edge of your car (the most likely place to run over your own kid playing in your driveway, or a cyclist, etc. And the hardest place to see by shoulder checking). If your mirrors are set properly, the remaining blind spot is ready to clear with a simple turn of the head.
If your mirrors are set in the deadly way advocated by several people here, you won't know where to look when shoulder checking, and worse yet, many people don't shoulder check at all because of that false sense of security. Meaning they have no clue what is in their new, and almost impossible to check, blind spot.
Anyway, it's obvious I can't convince people here to drive safely, so I only hope that the people advocating such dangerous behaviour aren't driving anywhere near me or my family. I'm done responding here, believe what you will, just stay away from me on the road!