Basically what others have said.
But sometimes I hear people saying that you HAVE to eat all your points, even if you're not hungry. I don't do that. I've never had more than 2-3 days in a row where I ate under points, and it's only when I've been actually ill that I've eaten under 20 points. (My target is 30.)
I'm trying to go off hunger cues. My body has a definite monthly cycle, and there's 2-3 days a month where I'm just not as hungry. Then there's like a week where I'm hungrier than usual. I guess it's hormonal. For a while I tried to eat my points, but since I wasn't hungry it usually involved me eating junk food, and that just seemed silly.