I'd say it all depends on how far you'll be tearing the engine down.
If your 'teardown' is going to be mostly cosmetic, like pulling it all apart, cleaning it up, painting, and re-assembly, then i'd definately try firing it up before hand to make sure there isn't any serious problems with the motor.
If you're doing a from the block up rebuild with all new parts and stuff.. well, i'd not even bother trying to start it.
If the motor turns free, it's very likely you could get it running with little effort, and decide to just hose it down with some engine brite and run it the way it is!
