That would fall into the same category as Elephants, Oxen, and Water Buffalo, most likely.
It really depends on their temperament. Since we don't have any alive today, you could probably make that part up and that will flow into what they would be used for.
If they are slow and thoughtful critters, you could simply use them for two things: Pulling (or carrying) heavy stuff, pulling plows, and for fertilizer. A critter that size could really enrich the loam, so to speak. This latter also kind of depends on the nature of the digestive tract, whether its more like a cow. If they poop cubes like regular wombats and they are that big, maybe look into the brick making potential.
If they are more aggressive, you could still have them pull large loads like Oxen, but they could also be used as war beasts. The purpose of a war stallion is as much as for momentum as it is for trampling and such. If they have claws that are good for digging or climbing that is a bonus. Their teeth might be a useful weapon in combat, destroying leather armor with ease.
Another note about the teeth. because they resemble beaver teeth, they might also be good for forest clearing.
Looks like a neat idea