The sharpening process is typically multi-step :
The honing step can be quite onerous if the size of the surface to be honed is large (every mm2 counts). Fortunately, by increasing the angle for the honing step, the area needing to be honed can be kept small.
Micro bevels thusly are used to make sharpening (and re-sharpening) of the tool faster, getting the craftsman back to work sooner.
What micro-bevel angle should you use?
The selection of the micro-bevel angle is not critical for the tool's sharpness, but it does impact the time required for re-honing the tool.
The tool edge depicted on the right has a micro-bevel, and shows dashed lines for the next 4 times it will be honed. As is shown, the lower angle micro-bevel makes for a larger surface area as the re-honing activities proceed. It is a bit exaggerated, but does show how the micro-bevel angle affects the re-honing activity.
Want more information on honing?
There is a very good guide on honing which was written by Charles Hotlzapffel titled, Turning and Mechanical Manipulation, Vol. 3 - Abrasive and Other Processes not Accomplished with Cutting Tools. This was originally published in 1850 by Charles Holtzapffel, and was later updated by Charles' son, John Jacob Holtzapffel in 1894. The 2d edition has 796 pages, of which 300 were revised from the first edition by John Jacob.