Replying to edge tuning and bevel

I won I little pocket edge tuner (This is it http://www.fktools-us.com/catalog/detail.asp?Part_Number=MT719#) and I want to start tuning my own skis. The tuner will do the side edge to one or two degrees and the base edge to one degree. Is it possible to get an original 90 degree tune with this? do both to one degree and I get a 90 degree, but repositioned? I think thats what the directions say. To sharpen the edge and get a side bevel Of one degree I do the side to 2 and the base to 1? What are the benefits of a base or edge bevel?