Sumo is a super slow and massively armored bot. It has the most Hitpoints among all T2 units making it the best choice for a tanking unit for your artillery.
In one-on-one situation it can even stand a chance against lighter T3 units.
It is equipped with a heavy laser that deals massive damage over an impressive range. It’s a precious unit in your army that leaves a big wreck.
Try to micro it wisely and repair it when needed.