Yes and no. The PV will run at full all the time (unless you have a rheostat on it), you need some way to regulate the draft on the stove based on temp. As the temp rises, normally you get more draft, the Baro can adjust for differences in air flow.
You should check it with a draft gauge to be sure, if you are staying within the .02-.04 range without changing the the power venter (speed that is), then you really don't need one.
It helps to control the slight variations of draft on the stove.