A lien waiver is the receipt the property owner wants: proof that the people who did the work have been paid for it and won't put a claim on the house. Owners and lenders ask for them with every draw and always before final payment. There are four common forms, conditional and unconditional, each for progress or final payment. A conditional waiver takes effect only when the check clears; an unconditional one is effective on signing, whether or not the money arrives.
A worked number
A GC collects a $30,000 draw and pays the electrician $9,000 of it. The owner wants the electrician's conditional progress waiver for $9,000 before releasing the next draw. If the GC paid the electrician $7,000 and asked for a $9,000 waiver, the electrician has just given up the right to collect $2,000, which is why subs read the number twice.
The mistake it hides
Signing an unconditional waiver against a check that hasn't cleared. Several states, California among them, prescribe exact statutory forms; using the wrong one can make the waiver invalid or, worse, valid against money you never received. A sub's job costing should treat a draw as collected only when it's in the bank, waiver or not.
In Obra
Attach each waiver to the payment it covers on the project, so the draw, the sub's invoice and the waiver sit together when the owner or the lender asks. Obra doesn't generate waiver forms; the state's statutory form or your attorney's template is the right source.