The buyer's inspection is where residential deals fall apart, and plumbing shows up in those reports more than almost anything else. A section of Poly-B nobody thought to look for. A water heater quietly leaking at the base. A drain that runs slow enough to get written up.
Each one turns into a price renegotiation you did not want or a conditional collapse you could not recover. Getting ahead of it turns those same findings into either quiet repairs before listing, or disclosed items your seller has already priced in. Either way the surprise is gone, and the surprise is what kills the deal.