Perhaps you need to move an aquarium across town, or even just across the room. As you empty it, the thought pops into your head that it would be a lot easier if you just left the gravel in it. It'd be easier to leave in some of the water as well, and you wonder what that might hurt, if you did that.
It's quite possible you can successfully move a small to medium sized tank with gravel, and even some water in it.
However, I would not recommend doing it.
Even though you may not break the aquarium, the seals will be placed under uneven stress. Although today's sealants are extremely good at holding the aquarium glass together, they aren't designed to withstand sheering force. Sheer force occurs when there is uneven pressure put on the seals.
A tank that is sitting on a well-supported level surface does not experience sheer stress on the seals. But when the tank is moved, the motion can put uneven pressure on those seals. If the tank is empty, that stress is not enough to cause a problem. But if the tank has additional weight from substrate or water, the stress created by moving the tank can break the seal.
The damaged seal might not be apparent until the tank is filled and later begins to leak. This risk is significant enough that most aquarium manufacturers will void the warranty on their product if it is moved with anything in it.
For that reason alone, I advise emptying your aquarium before moving it.
I confess that I have moved partially filled aquariums, particularly with small inexpensive tanks, but I knew when I did it that I was taking a risk. I don't think I would do it again, as it’s far easier to empty the tank up front than to replace it later because it leaks.