Without putting any good/bad attributes to mentally masturbating, and just looking at one of the after-effects, mental exhaustion, you can catch my meaning. I do not want to be mentally exhausted when I visit with my girlfriend, so I tend to not mentally masturbat often when I plan on seeing her. It would be unfair to her if I were too tired to share in mental stimulation with her, because I mentally masturbated all day long without her. Thats part of our relationship, this mental stimulation.
In no way did i try to imply it was bad to mentally masturbate, just was pointing out the reason why I don't do it too often.
Sorry for the misunderstanding :)