Most usage rights are time limited: a brand can run the content for 90 days, six months, or a year, and the rights expire after that unless the deal is renewed. Perpetual rights remove the clock entirely. The brand can keep running the exact same video as an ad or on its own channels indefinitely, and the creator has no contractual way to pull it back.
Because perpetuity removes all future negotiating leverage, it should carry the highest price of any usage term and be named explicitly in the contract rather than implied by a vague "unlimited use" line. A creator who signs away perpetual rights at a standard content fee is effectively giving the brand a multi-year asset for a one-time payment.
On Socialync's job board, every listing states the licence length before a creator applies, either a fixed number of months or, when the brand wants perpetual rights, that is stated on the listing too, so the creator can price and accept the term knowingly.