Blueprints don’t fail, people really really often do though. People measure wrong, or build on the wrong side of the line they’ve drawn. It’s not a question about “Is it essential”, it’s a question about “Will it make it easier, faster and less errorprone”.

I’ve worked in construction, and now work as a CAD specialist, so I know your pain, but the problem with “how to actually put a building together” is a very wide issue, also present with engineers and architects.

I read an article about it a while ago, and that said it’d be tethered to the ground, and power would be transfered through the tether.

It would be incredibly useful in construction. Having a digital overlay telling you exactly where to put up the framing for a separating wall, or an overlay showing the correct distance between screws, or where wires and pipes are inside a wall? There are so incredibly many awesome possible uses for AR in construction.

Why would the car already be at the car wash if you ask it wether or not you should drive there?

Sure, but only if it instead gives people a type of incurable cancer in about 30 years.