When installing surround sound, this setup allows a bit more flexibility when it comes to positioning the rear speakers versus a 7.1 channel system.
The rear speakers in a 5.1 channel system can be placed directly behind or off to the sides of the listener (i.e. behind the sofa, on two end tables on either side of the seating position, on the rear wall behind the listener, on the side walls to the rear of the room, and even in the rear corners of the rear/side walls at a forty five degree angle to split the difference.)
The point is, you can experiment with the sonic differences and with what is more aesthetically pleasing for the room in question. You will likely find the perfect place for your surround speakers.
For those looking at a wireless surround sound system, the 5.1 channel configuration will prove an easier install as well as far easier to find when shopping around.
For those who feel that they are selling themselves short by not going for the full 7 speaker setup, remember that today's sophisticated surround sound receivers that utilize 7 channels are designed to convert all content recorded in 7.1 surround sound to 5.1 speaker systems when needed. The sound for the additional speakers is simply routed to the two surrounds and you still get to hear everything. This feature found on pretty much every 7.1 channel receiver can be easily configured in the first time set up of your system after which you need not worry about it again. This is a great feature for two reasons:
First of all, most all HDTV broadcasts, DVDs,video games, and even Blu ray discs to date are encoded in 5.1 surround formats so you won't be missing a thing. Second,if your home theater system consists of a 7.1 channel amplifier/receiver, as more content becomes available, you can add the two additional surround sound speakers to your system if and when you wish to do so.