Nothing wrong with powering things because you expect them to have power while they're in your space. For big projects, that's probably the better way to do it, really - I haven't tested yet, but I'm pretty sure wiring a space gives it a measurable kilowatt-hour output, and while a regular house doesn't use all that much, big projects are not a regular house.

'It works because I say so' has either no upper limit or one we're not likely to bump into any time soon. 'It works because the space is wired for electricity' lets people bring their own plugs in and out, instead of counting on whoever made the room to know what your adapter looks like an build in a charger.