Electronics don't like surges. Getting hit by numerous small surges takes its toll on them slower than a single big one, but ends in the same result...you blow an IC junction or some other failure. Some things IN your house produce surges, and the closer to the point of use you can put the surge suppression, the better the protection. That being said, a lot can come from outside as well. That's where a whole-house suppressor can help. They generally have two important ratings: response rate (low nano-second is good), and peak energy (often measured in joules). The faster they respond and the more energy they can divert or absorb the better. You pay for those capabilities. Some also filter out noise, and that adds a bunch more to the costs as well. Having a whole-house suppressor won't absorb all of the noise or surges that a large motor can induce (such as an a/c compressor or other large load motors), so expensive things like computers and entertainment equipment can benefit from them as well.
As to cable boxes...sort of depends on who owns them. Building a decent filter/surge suppressor that doesn't phase shift or affect signal strength is not cheap. Do too much filtering on say a phone line and your DSL may no longer work. Anything that exits the house could be affected by external influences.
My approach was a relatively inexpensive whole-house device, and individual ones at expensive components. Your results may differ...