Someone is able to use compression and expansion to matter and space-time.
Law of preservation is still in effect so no matter how small the matter is, it will still weigh the same as if it was uncompressed, same with expansion.
I know that I can possibly create heavy nuclear elements or atomic heavy ones with compression of matter and make matter soft probably comfy enough if used with expansion
The question how useful this kind of magic/ability could be if I use it for industrial purpose or economic(Trading).
The scenario is Middle ages with magic instead of technology being prevalent.
The catch is now you're not a criminal, but instead, you're an artificer or blacksmith.
You must make sure that by any means that no fingers will be pointed in your direction that will make them think that your magic can be used for war, BY ANY MEANS NECESSARY.
NOTE: Since I can compress and expand space-time I have in theory an alcubierre drive. means I can travel FTL.