I think the intentions are good, but the result may not be what was intended. The idea of this "rule" is to prevent the senseless humiliation of one team by another, when victory is no longer in doubt. I've heard of this rule only in connection with amateur teams of youngsters.

Still, if I were a member of the losing side, I think I would rather remember having been creamed fair and square by a stronger opponent than to know the grownups had to step in and rescue me.

There are practical benenfits, besides the stopping of cruel humiliation, it may prevent injuries sustained by both sides for no reason. But I believe the hidden reason is that the audience, which comes to see a violent contest, does not like to see what violence usually leads to.