Well, it tells you the forces acting on the wings/undertray. This information isn't really that useful on it's own because you can't immediately work out how it well affect the car balance at speed. For starters, you need to know the wing positions and where the undertray acts, so you can see how grip increases at the front/rear relative to each other. With that you would get a good idea if certain wing angles will give oversteer or understeer. Tyre load sensitivity will also make a difference.
I don't use it, but then I made some better (the aero panel on GRC):
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In the end data analysis can only take you so far, final adjustments always need to be done from driving and tweaking until the car handles how you want it.