Does uncorrupted, unhallowed ground provide any advantages?

After a world enters hardmode, corruption and hallows spread relatively quickly throughout the land, bringing tougher enemies and better rewards. Does the spread of these biomes create disadvantages for the player, such as certain items becoming unavailable? Is there a reason to want to have vanilla biomes in your world?

I'm going to be cataloguing my findings here, don't hesitate to post your own answers.

Letting the ocean become hallowed/corrupted will make corrupt/hallow desert enemies spawn instead of ocean enemies, making the following items unobtainable: Shark Fin, Diving Helmet, Coral; their products will also be unobtainable: Megashark, Neptune's shell, waterwalking potion, hunter potion, diving gear, gills potion.

I like the music in the Forest biome =)

It's not a real advantage, but it's a big part of my gaming experience. And people seem to agree with me in the comments haha