For me, treat meals are a psychological necessity. I usually plan them around upcoming events, like a family dinner at a good restaurant. I notice that if I don't have a treat meal for a while, internal tension builds up and can lead me to overeat in an unplanned way.
That's exactly what happened yesterday. I hadn't had a bona fide treat meal in a while and had noticed a sense of lack building up inside me. Yesterday I was sick, so perhaps my defenses were down. I ended up eating about 3,500 cals of random stuff. I felt worse about this than if I'd planned to overeat.
All of which is to say: For those of us who are able to get right back on plan the next meal, I strongly believe in planned treat meals.