If you are like me you have a decent connection, know for a fact you're not utilizing as much as you're given and understand how a P2P protocol can help you and those around you.
But your average user doesn't really know what this all means without explanation. IMO most people probably have no idea what the optimal setting for them would be, therefore they will leave it on for fear of breaking something by switching it off.
Cool feature but let those who know better turn it on and let the rest of the masses opt in once their techie friend explains it to them and makes sure it won't hurt with regard to data caps.