If you have got a jacket with a belt, you do not want to leave the belt undone, because it flops around and is distracting.

Leave undone whatever you hesitate to do

Oh Lord, may I be directed what to do and what to leave undone

So you do not want scraggly beards, weird hair or anything else that people would be looking at instead of listening.

For women you would not want to leave your shirt undone, so that if you lean over you reveal something you did not want to reveal,

The important thing when it comes to grooming, as when it comes to clothes, is you do not want anything to distract from the strength and power of your ideas,