I guess if all else fails in a real bad firefight, his fellow officers can take cover behind his enormous bulk. Maybe endless jokes about what fat sack of turds he is will raise station morale.
According to Mythbusters, fat people don't actually stop bullets (and I'd hate to think of how much a custom bullet-resistant vest would cost to buy for him). He would provide concealment but no cover.
The Mythbusters experiment was just to see if a person's fat could protect their own vital organs (rather than those of their colleagues), and didn't account for bones and the like.
Amazingly, Officer Parent was able to subdue five men robbing the Bellevue Dunkin' Donuts. Witnesses say he flew around the shop like a spightly bubble bee, laying one man out after another.