I honestly found that the only technique I felt I gained in terms of specific things on rollers, was that one move - looking backwards. Yes, I got slightly smoother, but not even for me to consider it a really useful tool.

Others feel differently, some feel a LOT differently and swear that roller technique really is all that, and that's fine, just for me it clearly wasn't worth the time I put into gaining roller technique. (I exclusively use a trainer now.)

I had one episode where I did a lot of roller work only for 3-4 wks in the winter, and found myself becoming a terrible descender on a curvey descent that I was normally very comfortable with - turns out I was so used to riding stock upright on the rollers that any tilting immediately freaked me out! (It only took 1-2 rides to get my feel back on descents though, no real loss.)

If I were dodgy with riding a straight line though, or other riders commented on my dodginess, I'd absolutely work on rollers.

Oh, one other thing rollers will help your confidence in - close quarter riding - if you can ride rollers, you should have no fear riding even elbow against elbow full contact with riders left and right. (I was ok with that even before rollers from riding with roadies for awhile; I don't even comment if someone accidentally bumps into me if we're side to side.)