Not touching on any science here, but, these are what came to mind.
Transporting Cargo:
If they are able to "Expand" an area of space to a larger volume but keep the outer dimensions unchanged, then the technology could be used to increase the cargo capacity of the empire's ships. This way, a small shuttle could contain the cargo of a massive freighter ( depending on the extent of the expansion ).
Masking Military Movements:
Another use would be for the military to encapsulate a fleet inside one of these bubbles, which may or may not hide the ships due to distortions in space. It could even be used in conjunction with the above example, hiding a fleet in that small shuttle.
EDIT:
If the bubble were the size of a star or even a planet, then that empire would never have to worry about overpopulation as they could just use these bubbles to expand their habitable areas.