In many ways, yes I do feel as if I've cheated on my current partner but truthfully we both feel that emotionally getting involved with another person is the true meaning of cheating. At that point, it does become worth it because you feel that this new person is better than whomever you're with.
Love is numerous and various and though it may be unique, it doesn't have to be unique to an individual. Though I feel like most people who cheat are just bored or can't resist the temptation when the opportunity presents itself, I think Love still prevails above all whether cheating occurs at a severe degree or lesser.
So to answer your question, no it's not worth it and people do it because it's a wonderful expression of love/lust at the moment.