TL;DR
Make an option that prevents a belt to change it's shape by placing adjacent belts.What ?
Instead of placing a belt on another side like this:
Or this:

Make an option that lets you make it like this:

Why ?
Because there are cases when you need to fill only one side of a belt. Placing that reduntant belt makes it ugly and sometimes even impossible to fit.So besides convinience it would make some buildings more aesthetically pleasing.