Here's a few from me, but as I'm really tired the brain isn't in full working order - I'll probably jump back in later to agree with other peoples well thought out ideas
Pro's
- living as close to a natural environment as possible
- they get to see and feel the many changes throughout the day (the sunny spot at 11am, the night drawing in etc etc)
- fresh air
- freedom to choose whether to stay inside or come out to play (if you can give them the right size accommodation)
- they can make as much mess as they like
- they can see neighbouring bunnies (if you have more than one pair)
Con's
- we get cold going to visit them
- if they're poorly its harder to monitor them