I've already signed. Is a review still worth it?

Yes, but the job changes: it is no longer about changing the terms, it is about running the contract you already have without losing your rights under it. A review after signing maps out every notice period and time bar, the deadlines for telling the other side about a delay or a cost, so nothing lapses by accident. It flags the clauses most likely to be used against you with how to manage each, and turns a dense legal document into a short set of working rules the project team can follow. The terms are now fixed and cannot be renegotiated, but how much they cost you is still open, and that is what the review protects.

Say a fit out contractor has already signed and only afterwards wonders what they let themselves in for. A post signing review pulls out every deadline that bites: a five day window to notify delays, a fourteen day window to challenge each payment decision, and a strict format for both. Those dates go straight into the site diary as hard deadlines, and the two clauses most likely to be turned against them are flagged with how to respond. Nothing in the contract changes, because it cannot. But three months later, when a delay hits, the notice goes in on day four instead of being forgotten, and a claim that would otherwise have lapsed survives. The terms were fixed; what they cost was not.