Something I found with limited use of a plasma cutter is that a rough line can and will happen. The cut is so precise, unlike a cutting torch, that a fly landing on your hand will through you off. What I started doing is cutting just inside the line, oroutside, either way, cut towards your scrap slightly. This way if you suddnely sneeze, you won't put a big gouge in your good piece. Then I simply clean up the edge and grind back to my line. If you are feeling good, cut closer to the line, but I always clean it up quickly with a flapwheel and line it up with the line you were after. This is espcially true in light material where an error can happen really quickly.
I've heard the same about lesser shading for cutting. The welding store gave us some UV resistant safety glasses, shaded. They work, but if I cut a ong cut or repeated cuts, I was getting a white spot in my eye, and some irritation. Also, sparks and slag will smack your face sometimes. I gound that an auto darkening helmet woked better, at the lowest setting. No more eye burn, better face protection, UV protection, and it goes clear when done with the cut. Only problem is getting it to darken properly, as the arc is hidden from the sensor sometimes.