Pipe hidden behind the wall still has to be beautiful in relative to how the plumber have to work with it. If some plumber hide pipe behind the wall in a way that makes any maintenance impossible, then it's probably "ugly" for plumber standard.
Even if he is, to continue the analogy, people will care how well arranged and maintained those pipes are as soon as they have a problem with the plumbing and have to call a plumber.
A messy unfathomable array of pipes will cause the plumber to spend more time fixing the problem and will cost the customer more.
A well arranged, "documented" set of plumbing will help a good plumber spend less time performing the maintenance lowering the long-term cost of ownership of the plumbing. Not only that, it's more likely to work correctly the first time. Instead of spending weeks calling out plumbers to figure out why no hot water is coming from the bathroom taps, etc.