Since I have become a real Fitbit Ultra fan and have it with me every day, I am of course happy about every new feature. Depending on how much exercise I have, I have a certain number of calories available (i.e. for feeding). Accordingly, daily fitbit calculates live and foods eaten are taken into account.
Until now, it was the case that you were shown in the Fitbit portal "You have eaten X calories too much, please do more exercise […]". If you do that, it fits … But if you don't compensate for the calories you eat too much, the next day you're going to continue as normal – you've got (.B) 1800 calories available again (Fitbit Food Plan).
Now not (only) the daily calories are calculated, but also the data (food, exercise, etc.) of the last days. So if I ate too much yesterday, I'm also advised to eat a calorie-reduced diet from the Fitbit Portal (to be able to balance the previous day).