Our new house is on stilts. Underneath is a very small studio apartment. We don't really need an apartment down there so we have a few ideas:
Craft room-- has a kitchen so it would be perfect for getting water when needed or using the oven for Pinterest products(lol)
Tech room--computer and game systems.
Completely knock it all out and just extend the garage or leave it open so we have more space.
Pro of more garage is that we have more storage space and a pro of leaving it oven means we have more space for playing or parking cars