From what i'm learning about breaking in engines is that it is better to break the engine in the air than to bench run it. I can understand the first tank or two on the bench but I've been reading that some people run a whole gallon before they're ready to take it up. It would seem to me that the engine should be in the air for the break in because it needs to be cooled properly and running it on the bench would simply have more heat involved than it would have while flying.

Since heat is such a big factor concerning engine life and performance why do some people bench run engines?