P2P by default except on the enterprise edition, in which case it's local network only. They also claim to disable P2P if they detect your internet connection is metered (I'm not sure how that's done).
This is still a really bad default for the majority of users though...
Metered connections are a per-network setting that you have to set manually, not something they detect automatically. I highly doubt most users will be able to discover this feature since it's buried rather deeply in network settings.