I have some bought cause I saw it on a sale for next to nothing. I'll probably use when it's time to repaste my CPU, or replace my AIO cooler. Whichever comes first I guess.
Honest question: I’ve never reposted any cpu ever. Now I don’t run high end shit just session grade shit. I don’t ever pull the processor or the fan unless it’s dead. Even then I just scrape off the paste and reapply because I’m fucking lazy. The machine has continued to run for years. Again not the blazing heat generators that some are, but is it needed in most cases?
Depends on your cooler (or really more the socket which determines the amount of pressure the cooler puts in the IHS) and the paste you use. Some thermal paste, especially high performance ones, are more vicious. Over time with the pressure from the cooler it'll "pump out" as they call it.
Even if that doesn't happen to you, paste will dry out and reduce its effectiveness. Neither of these are a concern with PTM phase change pads. Those things will last for years.
I'd look to replace thermal paste like every 2-3 years or so, or if you notice your cpu temps climbing.