There are so many channels because you may need them. we all know that WiFi should be on channels 1,6 and 11. I ran into a problem the other day installing an Aruba system at a clients house. Their neighbors system was on 2 and 7. No other wifi was within range of the house. This meant that the best scenario for me was to throw all three access points on 11, or put them on 2 and 7. Since I had Sonos, I put Sonos on 11, and put the AP in the basement on 2, AP on first fl on 7, and AP on second fl on 2.

The reasoning for this is that Access Points can handle Co-channel interference much better than over lapping channel interference. I could have just gone to the neighbors and asked to adjust their system properly, but that wouldn't be right.

Since we really should only be on 1,6 and 11, it doesn't mean that we cant use the other channels. Using 1,6, and 11 allows you to utilize three channels without over lapping. You can use the other channels, but you would only be able to utilize 2 channels. If it was a high density area, this is not ideal since most people will be on 1, 6, and 11. Having the extra channels does allow you to compensate for other peoples stupidity.