You have the right to use it to watch cable. You don't have the right to set up a sattelite feed, to play video tapes on it, et cetera. That would require another license. Most people don't notice the difference. Many technical people do, and for a very specific reason.
People regularly modify their car for speed, handling or style.
Techies will try to rig their computer up to the house, so that it turns lights on and off. This ability lets us innovate more, because we habitually do so. Licenses expressly forbid us from doing so. The right to rip something you own apart and turn it into something new is very dear to the techies that are buying a lot of this stuff. It greatly changes the balance of rights and power from the consumer to the vendor.