The title of this blog clearly refers to this by Astargirl.
True, it's not easy to pose and to concentrate on the technical issues at the same time, but it's necessary sometimes. It's similar to the situation when a film director appears in his own film - well, it doesn't happen often, does it?
Personally, when I try a new photo technique, lighting, post processing, I first try it on myself. When I am comfortable with it, I look for opportunities to practice on other models.
This is how this (first in my portfolio) 'clone' photo has come to life. As you can see, it's sometimes difficult to get along with yourself :) :)