I don't follow MFP's advice not to track exercise on fitbit. If I log exercise, I log it to fitbit directly and that works better for me. I think the reason MFP suggests logging it here is because MFP will log it to fitbit for you so your workout shows in two places. Something to be aware of--if you log a workout to MFP then whatever you log replaces whatever fitbit estimated (just like if you logged it to fitbit directly). I mainly log an activity if i feel the calorie burn needs to be corrected or if it is an activity fitbit does not track well. If I log walking or running, I often lose very active minutes and it sometimes changes my step count. The calorie burn is usually about the same between my fitbit and heart rate monitor app for walking and running--the exception is if hills and steep inclines are involved.

I have noticed that if I go for a run or a walk, then Fitbit will automatically transport that over into MFP as "calorie adjustment". I don't bother logging it since it's already tracked.

If this link works, that Fitbit adjustment showed up automatically when I synced - http://www.myfitnesspal.com/exercise/diary/parker313_99