PX4 flow sensor for position control with GPS?

Hey guys, I wanted to ask about the benefits of using a PX4Flow sensor on board my aircraft along with my Here2 GPS.

Is there any benefit to using it AND the GPS? will it stabilize position hold more tightly in the air? or does it only work in GPS denied environments? also, if I do have it enabled in a GPS environment, will the PixHawk hand off control to the flow sensor when the aircraft is getting close to the ground to land? or will it still natively rely on the GPS?

these are just some questions I have that I am hoping somebody can answer