Description
Just like pools make posts in sets be able to be ordered. I'm not so proficient in coding and didn't see the site code but maybe it could work with almost copy paste of the implementation from pool to sets.

Why would it be useful?
Not everything has a generaly accepted order like a comic for example but many times a subjective one which would become possible with this feature to realize.

What part/s of the page/s would be affected?
set interface - you would have an order button at the bar and the ordering UI

And this. I really want this. It's so annoying if I put a work in the wrong set accidentaly or have to search for one post because it gets thrown in there in the order of upload and not in my prefered order.

100% agreed.