I’ve used a red dot mounted on a spotting scope and it was much easier to get to a specific point. On a rifle, I would think it helps inexperienced shooters that don’t have a good target acquisition technique when shouldering the rifle. I’m guessing the biggest downside, other than weight and bulk, is it trains someone to line up based on an offset optic, complicating what should be rather instinctual and simple.
Shooting prairie dogs, it’s easy to see which shooters have good acquisition skills with high magnification and which hunt side to side in the scope - the longer you do something like this the better you get, but good technique from day one greatly shortens the learning curve.