Than that in this business it is more? Pluss or minuses? Whether it is necessary to be protected by such simple image from copy-past?
It's a bit pointless. It'll take someone who really wants to copy your content seconds to find a way round it.
I agree with magda. Disabling the right click does very little to protect your images. That only protects you against the most amateur website owners who are not really a threat anyway. Sometimes this just ends up annoying real visitors who may want to save one of your images for other reasons. What is they just want to copy and paste something on your site but they are not familiar with the ctrl keyboard shortcuts?