Why trends work
A trending format or sound is temporarily over-weighted by the algorithm because engagement on it is high. Using it is borrowing distribution that your account has not earned yet.
The window is short. By the time a trend is obvious enough that you have seen it several times, you are usually near the end of it.
The rule that keeps it from backfiring
Only use a trend if your version says something you would have wanted to say anyway. A trend used as a vehicle for a real point reads as timely. A trend used because it is a trend reads as desperate, and the audience it brings does not stay.
Audio and formats
On TikTok specifically, trending audio meaningfully affects distribution, which is why the platform's own posting API can attach a trending sound automatically. AttentionPilot turns that on for carousels rather than making you pick one by hand.
Do not let the tail wag the dog: the audio helps a good post travel, it does not make a weak post good.