definitely agree with Porgeous. I know have monthly weigh in's with CDC and have my next WI on Wednesday. I think it is definitely the best thing for me! I have kept an idea on my weight loss on my scales at home and if you take last week (5th week) it looks as though I only lost 0.5lb that week, yet weighing myself today, looks as though I have lost about 4lb already this week and it's not over yet! So, when I get my weigh in results for the month on wednesday I will feel good, whereas if I had my official weigh in last week and really had only lost half pound, I would have been gutted.
Not sure if that's made sense, but in essence, everyone is different in their weekly losses, but you should lose a stone a month, so don't be put off if one week you have a low loss as the next week will make up for it x