Minecraft wiki entry for Best_biomes_for_homes, associated text: Has particular generated structures — Villagers can be traded with, and provide farms for the player to use early on. However, they also attract illagers and zombies, both of which will attack the village in raids and zombie sieges. This, in turn, can endanger the player, but also the villagers, which may even get wiped out in these attacks. Other generated structures can be looted for their resources and even converted into homes, although each structure will come with its own dangers.
Has particular mob spawns — Certain biomes have enhanced spawn rates for mobs, or they can be the only locations where unique ones spawn. For example, in the overworld, swamps are the only overworld biome where slimes, which the player can farm for slime material, can spawn at the surface. Mooshrooms only spawn on Mushroom Islands and its variants. In the Nether, endermen have greatly increased spawn rates in warped forests.