>>8430385like a previous person said it gives you options, you can keep the eyes transparent while painting everything around it black or whatever with the technique you prefer, also allows you to install LED units into your kit more easily.
I prefer just painting my eyes with metallics like I did here, looks a bit better than stickers and the raised detail really helps making it easy to paint.
you can totally put stickers behind the eyes as well if you wanted to, some people do that.
