Well I main Prot so I will pick Dps centered talents and rage abilities to help with kill speed solo. I think most will pick Dps oriented talents across many specs like this. Then for Groups or late game respect defense to tank dungeons.
If Gold is a concern then yes, don’t waste gold if you don’t need the ability.
I get the best spec available for what I want to do.
When leveling I only buy the spells I’m going to use to save money. I’ll purchase the rest at max level. This rogue still only knows instant poison though. I’ve never used any other poison so I’ve never needed to train the others.