Surge protectors are rated in joules, that rating is a cumulative figure. It will take that amount of joules in surges once, or over time. There is an indicator light on them that is supposed to indicate when it is no longer working. That does not always work, even with the really pricey ones. There are some really good test results out there on them. Even the ones that have fault indication that does work it does not work all the time.
Most modern household electronics of any decent quality will have some surge protection built in. It is the #1 cause of power supply failure. To protect the protected power supply use a surge protector. They are way cheaper than buying a new power supply for your LED TV and way way cheaper than paying someone to put a power supply in your LED TV.
Another option is using decent UPS systems as the good ones have surge protection built in and they are power conditioners by nature of their function. You can get some really good ones these days for what I consider to be a decent price. I have them on my main PC and on the living room entertainment system. Which is several computers and a nice TV.
So, how often? It really depends on how many surges/micro surges they take.
I replace all of mine every 3 years, and sometimes on the pricey stuff after storms that have close strikes. I often will take the old ones out to the garage to use as power strips until they finally give up the ghost.