Think if it this way. The GRCS is like using a 90-100cc saw when you could get away with using a 60cc. It's not going to come out to play often, but when it does it saves from having to do all the tricks needed.
Like Mugg's mentioned, its great for preloading and static weighted rigging. Sure one can do the same with a 5:1 and a porty, but no where as gracefully. I'll still use a 5:1 and porty, and a 60cc saw double cutting bigger wood. But its a great tool in the box when you need it.
@Muggs I had the same hesitancy, other than using a GRCS on a previous crew (and I hated it!). We only used it a few times, and really only for pulling back leaners with the hand crank. GRCS vs Hobbs? Both great tools, I haven't used a hobbs. It boils down to if your using it as a bollard lowering devise, it does the pretensioning well. They both do the pretensioning well, but the Hobbs is better for lowering, and the GRCS is better for winching. Of course there is the GRCS bollard, but it doesnt pre tension... Also from the sounds of it, the hobbs should have two folks on it if any real winching is done as it doesn't self tail.