Recently I was working with a Snapmaker Artisan and using the CNC module to cut a simple PCB from copper-clad FR4.
For best results, the cut board needs to be lightly sanded and cleaned up. But I wanted to check how clean the cuts ended up -- any stray copper or rough bits of cut would cause a short. It's necessary to inspect the quality of the traces.
I stumbled upon using a UV illuminator to shine on the PCB. Because FR4 (the PCB material under the copper) glows under UV, it is very easy to see with the naked eye whether cuts are clean or not. Previously I was using a magnifier and lots of light, but shining some UV is so much easier.
Clean CNC cuts show up as clean, unbroken glowing lines. Any debris or rough edges or stray bits of copper (if there are any) are easily spotted as a result. Just a quick little tip!