perhaps more consistent a/c performance? If the fan shuts off when the compressor cycles, then the condensor stops cooling off, and even begins to absorb ambient and/or engine compartment heat. When the compressor kicks in again, and the fan restarts, there will be a lag before the condensor is again fully cooled. Kinda like what happens when you first start your truck on a hot day, or after it's been sitting in the parking lot for a while. It takes a little bit for the a/c to get cool. That is the time it takes for the condensor to start cooling off, and in turn, the lag time for the evap to start getting cool air into your HVAC system.
Actually, I think I like this idea. When I install my electric fan, I think I might wire it to do this; go full speed when a/c is selected, regardless of compressor engagement.