Rules:
*You can teleport into and out of it at will
*It has a couple of plug sockets and can connect to internet from the region you teleported in from
*You can take objects and people with you
*As already stated, it is (3m)^3 (3m*3m*3m). The walls are plain plaster with a light in the middle of the ceiling. The pocket dimension is topologically toroidal, so if there weren’t walls and a ceiling/floor (which you can actually destroy) you would loop if you went more than 3m in any direction. Gravity, then, is artificial and can be altered to anywhere from 0 to 2g from a dial on the wall.
Edit: additional specifications
*You can only teleport out to where you teleported in from.
*Time proceeds at the same rate inside the pocket dimension
*There is an eject button for those inside to get out if something happens to you
Free electricity? Mining crypto with a lot of stolen hardware.
Smuggling would be easy for reasons already mentioned.
Murder would be easy. Teleport someone in, teleport out all the air.
Escaping from robberies and hairy situations, likewise creating hairy situations.
Sleeping in 0g sounds comfy, training at 2g sounds awesome.
Living rent free on every city ever. Paired with a car means I can be everywhere.
Huge portable storage box.