While that is not the only purpose, but it's true that most of us visit it a few times around late pre-hardmode, early-hardmode, and then not really. On vanilla at least.
Just compare it with other biomes, like the jungle. you probably spend some time there pre-hardmode, maybe looking for componants of jungle armor, or some of the loot in trees/shrines. and hives to fight queen bee. then in hardmode, after one or more mech bosses down, looking for life fruits, then after all mech bosses are down, for clorophyte maybe, and then for plantera's bulb, and then loot the Lizhard temple... and who knows what else. You also need a bezoar for the ankh shield too.
in comparison, you visit the underworld only a few times, around the same time. mining hellstone maybe, getting some stuff like a hellforge... if you already looted the dungeon, you can get all the stuff from shadow chests too. You might need a hellbridge, but if you have lava vaders, you can go well without building a bridge too. there are a few cool drops, but only a few. after you defeated WoF you can stay a bit and look for the tortured soul and purify him, and that's pretty much it. you can go back later if you want to fight red devils, or if you're looking for adamantite/titanium which likes to spawn near hell, but that's pretty much it... (in vanilla), I think.