I love using mundane animals as a way to portrait environments: a forest needs wildlife, a farm town needs sheeps and cows, a city needs dogs and cats and pigeons. Also, I like to use mundane animals when I don't want an encounter to be a combat but I'm afraiymy players will default to violence: if I put an owlbear the players will be more inclined to fight if they feel threatened than with a mundane bear. And my players love having mundane animals travelling with them: horses as mounts, a hound to help keep watch and track foes, a cat just because why not?
On the other hand: I just rewatch The Last Airbender cartoon and I'm thinking if the next campaign I run should use only "weird animals" as the mundane fauna. Megafauna, dinosaurs, impossible hybrids, etc.