You know what I have always weighed myself every day or every other day (When im trying to lose weight) and have found it to be so negative in terms of me personally sticking to a plan. I found that I would feel like i'd lost, get on the scales after 2 days of being good and they wouldnt reflect how I 'felt' which would leave me in bits thinking s*d it, I cant do it!!
Now on the other hand as part of my 'new year, new me' thing im only weighing once a week, same place, time, routine of wake up, wee and scales. So far ive seen a loss each week and havent felt demotivated.
I suppose its what works for the individual... but I know that checking any more than once a week is such a negative thing for ME in terms of my long term goals... thats not to say that I cant understand why people have to do it.