there are different schools of thought on this one, your weight fluctuates so much during the week naturally anyway that it can be really demotivating if you see a gain when you know you have stuck to the plan, therefore it is better to just get weighed once a week, however the other school of thought is that sometimes what can happen is you may have just one of these fluctuations that falls on your weigh day and if you've not weighed yourself all week you then think you have gained overall over the week, when this may not be the case and if you weighed yourself the next day you would have lost. If you do weigh yourself daily, you will see a pattern of the fluctuations, but I tend to be inbetween and weigh myself a couple of times a week instead of just at weigh in and take a gain with a pinch of salt if I know I have stuck to it
I do think it is about time SW stopped focusing so much on weight loss/gain alone and also measure body fat % in conjuction with weight