I have just one for Crafter and hotswap the weapons (the rest of the gear is identical so...) and used to for Gatherers...not sure why I stopped doing that and made them each one, honestly...
...but yeah, I also have Bozja and Eureka sets for my mainly played role (Healer, but if I did other roles, I could see myself making a few more), and a lower level gear set with a different glamour for when I want to PvP in a different outfit or Job specific outfit (WHM robes, SCH robes) than I use for my level 90 gear (since I omni-Healer [and play a couple Tanks, SMN, and RDM], I try to pick a set with no Job-specific gear so it won't go stupid looking if I swap Jobs in a place I can't change my glam)
So yeah, there are reasons to have more than just number of Jobs/a few extras.
