Why would engineers and architects need to find angles in a polygon

As a engineer who was mechanical then electrical most buildings, schematics,etc require some form of calculation for some shapes seeing that those shapes are what make up the world. Say for example you need to make something like a mother board pro house knowing it's shape and angle helps make a more accurate structure during the blue printing and build phase. No one just goes in and wings it you need to determine angles for things you don't know that the point of it.