Purifying the entire world with making contained areas of Crimson/Corruption and Hallow is a very long and tedious task. And since citizens can live in Hallow, and normal enemies are not obstructed from spawning in Hallow.
Is it a good solution to make the entire world Hallow? Jungles will not be consumed because Hallow does not spread through mud and/or converts mud to dirt.
The only problem I see is that desert and the normal green biomes will no longer be existent (I can of course make quarantined areas of that too). Are there any unique features/items in the normal Green and Desert biomes?