I think it depends on how your individual mind works. If you're the type of person who falls into the trap of thinking that because you went off plan/diet for one meal, you might as well make a day/weekend of it, then it might derail you for a bit. If you're the type of person who figures one off-plan meal is no big deal and you get right back on the horse (or beef as the case may be), then go for it.
"Right is right, even if no one is doing it; wrong is wrong, even if everyone is doing it." - St. Augustine