I... don't quite see how it's a bug, honestly: if the belt is full, you should not be able to place another iron plate on it. And indeed, you can't. What's the bug?
A somewhat valid use-case is for inserting science packs into labs.
There are seven kinds of science packs in the vanilla game, so without sushi belts, you need four belts to bring all of them to the labs. That can take a lot of space, making it harder to for instance use beacons (which like compact designs since their effect range is limited).