i'm not as experienced as a lot of the people on here, but here's my take on it.
i believe in the "foot in the door" theory in social psych...basically by letting in a scheduled cheat meal you're kinda opening up the door to that kinda thing creeping in more often. "well, i had pizza yesterday, but only one slice so this brownie will be the second half of the cheat meal." see what i'm saying? this may not be true for you, but i have had that sort of creeping problem in the past, where a lil cheat gradually grows larger and larger...that being said, i don't think it's bad to cheat a lil bit every once in a while. i do incorporate sweet potatoes in my diet maybe 2-3 a month. i also eat more fruit than a lot of the people on here, but don't consider either of those foods cheating, but some very strict PBers would. my cheats have been (after almost eight weeks) - one organic cream soda which i wouldn't take back for anything. it was so delicious and beats the shit out of diet coke any day! an a sliver of my sister's birthday cake and a scoop of my mom's homemade vanilla icecream.
those weren't scheduled, just happened...random. so instead of every saturday for dinner i have a wicked blowout maybe have a few lil cheats every now and then when you feel good about it.
i will maintain the truth
i knew naturally as a child
i won't forfeit my creativity
to a world that's all laid out for me
i'll look at everything around me
and i will vow to bear in mind
that all of this was just someone's idea
it could just as well be mine - ani difranco