With an adapter, you can hook up your MBP to your TV to watch. With your iTunes account, you can transfer your purchases onto other devices you own.
Personally, I only rent movies from iTunes, and if I want to buy a movie, then I'll buy a Blu-Ray, which also comes with a digital copy.
If the Apple TV was a lot cheaper, then I would be more inclined to purchase movies from iTunes. But as of right now, I'm not going to pay that much for a little box which only use to me would be to rent/buy movies from iTunes. Apple started going in the right direction with the Apple TV, but it needs to be A LOT cheaper. Like half of it's current price. Or, another option would be to create an iTunes for the PS3, XBox 360, etc. I have a PS3, which I don't use for games, but only for movies and tv shows. With the Blu-Ray player and easily upgradeable harddrive (I installed a 320GB), there is a far greater value in the PS3, than the similarily priced Apple TV. If I could get iTunes on my PS3, then my world would rock.