Qusetion: Shimano STX RC rear derailleur
 

I reciently purchase a use Trek 1000 which has the following drive train setup:

Sora STI 3x8 speed
Bontrager Crankset 170mm 52/42/30
Sora Ft Derailleur
Shimano STX RC rear derailleur (changed from original)

I wasn't familiar with the STX RC rear derailleur and after some checking on the web, found out it was typically used for mountain bikes. Does anyone know what the advantage is to replacing the original Sora road bike rear deraileur with the STX RC? A test ride of the bike found that the set-up shifted just fine (needs some fine tuning). Do I gain anything by converting back to a road bike specific rear derailleur? If so, which one would you recommend.

Any information would be most welcomed. Thanks

This is usually done to use a rear cassette with larger gears, like 28 or 34. Is the bike geared really low? It might just be for cost too.