Is there a critical difference for, eg, tom growing,?? = Tim
Two come to mind.
Price. Growbags are a lot cheaper than bought potting compost.
Nutrients. Growbag medium usually doesn't have many, that's one of the reasons you need to feed toms so hard, potting compost usually has more nitrogenous feed which is OK for toms until the first truss sets, but thereafter it's not what you are after - lower N, higher P & K is desired.
Thanks! = Tim