The two basic types of protection are "whole house" and "point of use". Types of surges include "ground seeking" (e.g. a lightning strike, or a MV phase contacting an LV line, etc), "differential", and "inductive".
Point of use protectors protect against the differential surge, which is the most common at the point of use. As all voltage is a difference between the potential of 2 points (conductors in this case), the protection is to minimize and limit this voltage difference. That difference can exist not only between line and neutral, or between lines, but also between any of these and EGC. Additionally, the voltage difference can be between anything else metallic (cable coax, antenna feed, CAT5 to network, twisted pair to the telco, metal water pipe, metal gas pipe, A/C freon tubes, heating ducts, metal building frame, etc). A scary long list!
Correct protection at point of use is to interconnect every metal together so that the voltage potential is minimized. The closer connected, the better. Since direct connection isn't practical (fault currents on power, lost of signal on communication wires), the metal-oxide varistor (MOV) device is substituted as the best alternative, since it will have a high resistance at low voltage, and a low resistance at high voltage.
Everything must be connected. Leaving some metal conductor out of the protection does not leave you partially protected ... it leaves you unprotected. This is because electricity does not just flow over the least resistive path. It flows over all paths it can access. So even if you have proper protection for your TV on the power conductors with a POU surge protector (power strip), damaging currents can still flow from the rising voltage on the power (if that's where it comes from) to the cable TV coax or the satellite dish coax (through the receiver/converter box, and out through that coax).
The coax and phone connectors on the power strip protectors are not there as a selling gimmick to make people think that gives them other options. They must be used if those kinds of cables are present and connected.
Whole house protection works similar to point of use protection, but on a larger scale. However, because some surges can occur inside the house for various reasons (such as an inductive surge from a lightning strike on a tree at the opposite end of the house from the service entrance), the whole house protector is not a substitute for point of use protection. Even with whole house protection, you get more protection by also having point of use protection.
But even whole house protection needs to be done right. That means everything metallic must come in together at a very close proximity. And this can be hard to do with some code requirements for minimum spacing of things like an entrance meter and a gas meter. The whole house protection can be ineffective if there is an alternate path for the surge to exit. Cable TV must come in at the service entrance. The phone line(s) must come in at the service entrance. The antenna feed must come in at the service entrance (and this gets tough for amateur radio operators who have their "shack" inside the house ... so I recommend hams have a real separate shack where possible to simplify the antenna wiring). Water and gas also need to come in there as close as you can get them, and be well bonded with large conductors to the same grounds as the entrance panel and protector are connected to, closer to the protector.
Both whole house and point of use protection work on the principle of equalizing the voltage potential so that the difference between any two points is reduced. When a surge event happens, the entire house can rise in voltage relative to earth perhaps many thousands of volts. As you know, it is not the voltage that kills, but the current (and it doesn't take much). It's the same for electronics, with some devices being damaged by even less current than would kill a human (though many other things would need a lot more current).
Whole house protection can also protect against common mode surges with fast rise times. But these surges will weaken quickly as they travel over the conductors due to the induction that would be present for current flowing in a single direction without a return current. A well grounded whole house protector can generally protect against a direct lightning strike on an in-air service drop. Beyond that, the inductive effects of the cables will reduce the first voltage rise (high frequencies are impeded much more by the inductance).
