If you are following a weekly average TDEE method (and if same amount daily then you are) - you should NOT sync the Fitbit.

MFP is going to take that daily calorie burn, subtract what it estimated your daily burn would be based on activity level, and then increase or decrease your eating goal by that difference.

Fitbit 2400 - MFP 2000 = 400 adjustment.

2000 eating goal (your TDEE - 15% say) + 400 = 2400 new eating goal.

Now - if you just want to memorize 2000 (that one is easy) and not care about in the red or in the green - then fine - but your macro's will be messed up too.

Unless you are paying MFP for the membership and set the option to NOT increase calories from synced devices.

Best use of Fitbit is merely to look at your weekly emailed results, and confirm the TDEE is about right, based on what you do instead of guessing what you are planning on doing.

Only caveat would be some exercise should be logged on Fitbit for accuracy, depending on the workout, your Fitbit model, and how long the workout is.
For instance if I didn't log my long bike rides manually - Fitbit would be short by 500-700 calories on 2-3 days a week.
That would give a terribly under-reported TDEE in my weekly email, and if I based eating level on that, AND took a deficit - I'd be badly under-eating.

I find syncing the device to MFP gives more headaches than it is worth.
I would just use the data from your fitbit, showing you what you a burning daily, but leave it unsynced to MFP and manually do your calories on your diary.
I set my tracker to TDEE and if I track any activity, then the calorie burn is changed to 1. that way I know daily what my tdee is and what i need to hit and not worry about the outside forces messing with that:)

Kelly
EM2WL Ambassador and Moderator