What is UML ? For me, it is a way to describe the architecture of your software. It gives basic diagram type. Yeah, you can be a purist and do UML in the pure way, but for me, I use it only as everyone knows how to read it. Same as a map, it gives you direction.
Why UML compare to simply exploring code ? I always find more interesting to have partial maps of my code with only specic area of interest and/or dedicated purpose and share this to others. A beginner would/should be interested in those high level maps before jumping into the code. A expert in that area shoudl not need it.
But if you modify the map... it should break something ! Usual UML document are out of sync unless you have a strict handling of those documents in your team.
Thus this simply idea of creating code maps via UML concept using your code and ensuring that a key change should trigger a review/break change !