Join Date: Aug 2007
Location: White Lake, Michigan
1/8" roundovers will just "ease" the edge... it'll get rid of the sharp edge of the board and save you a bit of sanding, no matter what the stock's thickness is. As you go larger, more wood is removed and the side profile of the board becomes, obviously, more rounded over.
Depth of cut also influences what the finished product looks like.
IMO, It's something you really have to experiment with in order to fully see what they do. Go to town on some scrap wood to discover each bit's abilities... then you'll be able to easily decide which bit to use for the job at hand.