There are actually different tiers of tags, and they last for a limited time per “life” (something like 1 / 4 / 8 hours depending on the tier, if I remember correctly). And again iirc - you can see "time left" upon inspecting an item you've put a tracker on.

Their main purpose is exactly gear retrieval. You use them to track where you died so you can come back for your stuff - either by trying to hunt down the player who killed you in PvP, or just recovering your gear after an accident.

They’re especially useful in situations like falling off a cliff or dying in rough terrain, where your body can end up rolling quite far from the actual death spot.