@ cabbage dad
It isn't something that I would want to do a lot. I did experience a couple times in college the ball was never hit to 3b side but we did throw a quick runner out at home. Whether it helped keep the runner one step closer thus letting us make a close play I don't know.
I do know it probably helped my jv team once and our varsity team at east once. Haven't gotten stung by it yet.
I see it a lot on the high school level, and I don't mean once a game especially at jv levels.
To answer your question personally I think seeing it as regularly as I do, I think coaches are not confident in their kids moving during a play. When my college coach used it and when we used it, it was as a called play. In all the cases the 3b moves more like 1b as ball is pitched.