Finalising early, confirming receipt before the package arrives, releases your escrow to the vendor and removes the dispute path. If the item then does not arrive, there is no route to reverse the release.
Why vendors ask
Some want the money before the shipping window closes. A few have reasons that are legitimate for a vendor you have used many times. Most requests to a new buyer from a new vendor are a scam pattern.
The position
Do not finalise early on an unproven vendor. If a vendor pushes back on the refusal, choose a different vendor. Awazon locks finalise-early behind vendor probation for exactly this reason, and giving up escrow voluntarily throws that protection away.