Currency is a critical part, at least IMO it should be, of all D&D campaigns. Many campaigns spend a decent amount of time in cities shopping and searching for things. A great example is Critical Role. Hate 'em or love 'em, they do a great job showing why currency is important. There have been many time they went into a city looking for or wanting to buy certain items and they couldn't because they didn't have enough gold. This is D&D, not any other CRPG. If your players walk into a city looking for +1 weapons/armor, do you just say "ok you go and find it and put it on"?