7.1 or 5.1

One simple benefit is that it can provide a more immersive experience. Like when a live audience applauds at the end of a performance, some clapping comes from the rear, helping to create the impression that you are in the performance hall.

During the performance, some echo might be audible from the rear, suggesting that you are in a large hall and some sound is reflecting off the back wall.

And of course for movies, the back channels offer the opportunity for sounds from behind, like explosions or the snap of a twig as someone approaches you from behind.

You may want to post this question in the Home Theater forum as you'll get more responses.

Since this is the Analog room my answer is, why would you want more than 2 channels? Let alone 5 or 7?

Stick with two channels, that's the best.

Shakey

@.1 for music and 7.1 or 10.1 for video