Do I really need a contract review before signing?

If the contract is amended, bespoke, or simply bigger than you can afford to get wrong, yes. An unamended standard form, one of the ready made industry contracts like JCT or NEC used exactly as published, is a known quantity, but almost nothing you are asked to sign is unamended. The schedule of amendments, the edits bolted on by the other side, is where payment terms get stretched, time bars get sharpened into deadlines that can wipe out a claim, and liability gets shifted onto you, each change reading harmlessly on its own. A review reads them all together, against the law and against what is normal for this kind of contract, while you still have the power to change the wording. Once you have signed, that power is gone, so the value of a review is almost entirely in the timing.

Say a cladding contractor is offered their biggest job yet, worth £400,000, on an amended standard form. One clause at a time the amendments seem minor: payment nudged out, a notice period trimmed, a cap on liability quietly removed. Read together the day before signing, they show a contract that pays slowly, is quick to bar claims, and leaves the contractor carrying uncapped risk on a job they cannot afford to lose. Because they looked before signing, they can still ask for those three points to be changed, and the other side agrees to two. A week later, contract signed, none of that would have been possible: the review paid for itself because it happened while the wording was still open.