The fastest way to cut material is to use a round tool against flat material, and a flat tool against rounded material. The tool makes contact across a very small section of the stock, putting more pressure against a smaller contact patch. Dean Torges talks about this in his book on bowbuilding.
It's faster, but it's also more prone to putting dips and hollows in the bevel and complicating the sharpening process. I can see it if you are working a nick out, but other than that I will stick to a flat file.