[ff317]

I bought a new-construction place, and I was around during the process. After they were done with all the plumbing/wiring/etc, but before they filled in the insulation and sheetrock, I walked the whole house and took cellphone pictures of every bare wall to show where all the pipes and wires are run, and then labelled it all up by room. I plan to hand those off if I ever sell the place! I don't know why builders don't just deliver such a set of photos to everyone by default, it's been super handy!

[Mtinie]

I agree it’s very handy. To provide one answer to the question in your final sentence:

“Closed walls hide many sins.”

[spikej]

Someone gave me an added tip to include a tape measure in the shots so you can more easily line up where things are after the wall's closed.

[femto]

Also keep in mind that wall studs are usually a standard distance apart (600mm or 450mm in Australia), so such pictures have an "inbuilt" tape measure.

[danofsteel32]

I am a custom home builder and we do this. It’s very handy when the drywallers cover up an outlet or switch.