You dont want to use more than 8% or your lather will be adversely affected and your bar will be too waxy. Its my opinion only, but I think its one of the ingredients that adds to a sort of sticky feeling that I call "hard water drag". But it can help you make a nice hard bar in small amounts.
I used 2% beeswax along with 10% cocoa butter for a lavender soap that turned out well - it is quite hard and shiny. I just washed my hands and face with it to remind myself what its like. Its very nice, although it does have a teeny bit of that "hard water drag" even after curing for 6 months and having clay in the recipe. It lathers well, cleans very well without being drying (for my skin anyway), and has been very popular - I need to make more of it.