Here's the deal. On a small, two stroke/four stroke motor, it won't hurt it at all as long as no oil/exhaust gets into the working/electrical systems.

Now. For larger, gas powered, especially single cylinder engines, that's a different story. When running one of the larger motors on a fuse only, there's quite a bit of vibration that can tunnel down the fuse and through out the entire system. With large airplanes especially with gas motors, swinging big props, it's always a good idea to have the wings on the airplane to dampen the vibrations.