Modern cable systems are large, with a single network and headend often serving an entire metropolitan area. Most systems use hybrid fiber-coaxial (HFC) distribution; this means the trunklines that carry the signal from the headend to local neighborhoods are optical fiber to provide greater bandwidth and also extra capacity for future expansion. At the headend, the radio frequency electrical signal carrying all the channels is modulated on a light beam and sent through the fiber. The fiber trunkline goes to several distribution hubs, from which multiple fibers fan out to carry the signal to boxes called optical nodes in local communities. At the optical node, the light beam from the fiber is translated back to an electrical signal and carried by coaxial cable distribution lines on utility poles, from which cables branch out to a series of signal amplifiers and line extenders. These devices carry the signal to customers via passive RF devices called taps.
The major network channels are all broadcast in HD. And you'll be pleasantly surprised to learn that the quality of uncompressed HD video in an antenna feed is actually superior to what you've been getting with your cable box. Cable operators have to deliver hundreds of channels, plus broadband and phone service over a single connection to your home, so the TV signal is usually compressed to conserve bandwidth. Not so with your OTA feed. The difference is immediately noticeable. Outside of a Blu-ray movie, this is the best output I've ever seen on my TV. And did I mention the channels are free?
The option that has become the standard at our house for watching TV, movies via Netflix and a variety of other sources is a software called PlayOn. PlayOn is basically a media streaming software that will pull the video streams from sites like Hulu.com, Youtube.com, network websites, MLB.TV, Netflix, Amazon Video and others and allow you to stream them over the home network, to a network media player attached to your TV.
The question of "when does it make sense?" can easily be rephrased as "how much money can I save?" and one of the biggest factors will be the price difference between combined internet and TV service or just internet. These are also the options that vary the most widely based on where you live, and the availability of promotions or contracts that can keep prices down for a short time.