Families can easily use multiple channels, even with only two phones. For example, your wife gets a call, then your son gets one from his girlfriend. You tell him that he had better go walk the dog, so he transfers the call to his cell and continues talking. That frees the phone but not the channel. Another call comes in for you. You've got three channels going, yet you'd still like to be able to answer a new caller via call waiting, or at least have him get voicemail. When you're out of channels, callers get a busy signal.
Of course, for a business, many channels may be required.
