I've just started doing this. But in fact I'm doing it to ensure that I'm getting ENOUGH calories. I'm a pretty active healthy woman and have always struggled gaining weight. Now that I'm pregnant (15 weeks) It doesn't seem to matter that I'm snacking all the time, I noticed I'm still lighter than my pre pregnancy weight!
When I started tracking what I've been eating I saw I was taking in about 500 calories less than I should be. This summer heat probably isn't helping me to feel very hungry - but less than what my baby needs is simply not going to do!
Love this site / service. Wish they would allow me to add a weight GAIN goal though.