MBP 15" retina: Discrete graphics card worth it?

Apart from gaming: Is there any other reason why I should buy a MBP with discrete gc?

In the shop a technician told me: "If you want to watch movies with your 15" MBP retina, then you need one with a discrete graphics card!"

=> But then a vendor showed me some youtube videos in 1080p with a MBP which had only the integrated graphcs card, and the video was absolutely workig well and smooth. That's why I doubt that I need a discrete gc for 1080p movies. (and according to the settings 1080p is the highes resolution avaiable on a 15" MBP retina).