What does a paid plumbing inspection actually cover?

With no known leak or fixture trouble, I’m not sure what would make a routine plumbing inspection worth paying for. Is it usually a walkthrough of visible piping and fixtures, or should it include accessible areas like under sinks, around the water heater, and near the main shutoff?

I’d also like to know whether checking shutoff valves or looking for signs of hidden leaks is normally part of the visit, or an extra service. I realize a visual inspection can’t rule out defects behind walls. If the plumber recommends repairs, what findings or photos should they provide so I can understand the reason and decide what needs attention now?