When using a loom, a bench can come in handy. Loom benches are adjustable in height.
If a table loom is on a low stand, you can work with an ordinary chair.
If you work on a loom that stands on a table, you need a high chair or a bench.
Pushing on pedals with the knees bent too much is uncomfortable and you can't use much force either.
That is why a loom with treadles is usually made higher, and is intended to be used with a high chair or bench.
When weaving on a loom with a large weaving width, a wide bench can be useful so that you can slide from one side to the other on the bench to access both sides of your fabric.