Manufacturing tolerances vary from industry to industry; a watch maker’s precision is higher than a house-framer’s. Motorcycle accessories fall somewhere in between.
For this reason, when installing parts with more than one screw, it’s a good idea to start each one in its threaded hole before tightening them down.
Leaving the screws loose allows you to align and position the part, reducing the risk of damage to the chrome finish, threads, and structure of the part or motorcycle (or train, plane, and automobile).
We all need a little “built-in slop” or “play” in our lives, it gives us room for error (read: being human).