A 'scope' generally refers to a magnified optic. There are red-dots that you can put magnifiers on, but I don't recall seeing too many red dot 'scopes'. There are scopes that have a 'dot' as part of their reticle (eg, the Primary Arms 1-4x rifle scope).
A 'sight' generally refers to an unmagnified optic - whether it is 'iron sights' or red dot/holographic sights.
With that out of the way, I use red/green dot sights exclusively on my 15-22s (3 of them). The reason is the distance to target is 100 yards or less, and the target size is 4" or less. An unmagnified red dot is fine under these conditions. It's lighter than a rifle scope, provides sufficient accuracy, and allows one to test their skills a bit more.
Good luck.