The more I weigh myself, the more anxious I get and the more obsessive I get. I know it seems extreme but the stress can actually cause your body to not lose weight (might not be the case for you but it happens to some).
And...when I weigh at night, I never know if my body is done processing dinner, the cup of tea I had, the 32 oz. of water I had working out.
Now I try to stick to mornings as I have an empty stomach and haven't had water or food for about 8 hours or more.