I guess the usefulness of this actor is if you, let's say, have a bin of pictures with many different resolutions, and then you're using the 'picture' input of the movie player to switch between them. If the resolution goes above a certain point, the Limit Resolution actor would jump in and ensure that the resolution is not too high.
On the other hand, a better rule of thumb would be to have all the pictures at the size you want them in the first place. So I guess I won't worry about this actor.
Best Wishes,
Mark