As Stephan said, it all depends on the HT and who is doing it.
I leave my stainless edges at .010". I take carbon to .020". Using an oven and proper metallurgical techniques, these thicknesses do fine.
Nowadays, Brad at Peter's does most of my blades. I still like to do 1084 and 1075 in the forge by eye. Hypereutectoid, stainless, and any steel with much alloy content is done in the Paragon.
In the beginning, most makers have several problems to deal with;
Lower ability equipment.
Lack of HT knowledge and experience.
Lack of grinding skills.
These all add up to needing a thicker edge in the beginning. Many folks recommend an edge of .030" to .050". This removes a few of the variables from the HT and gets you down the road faster. With time and more experience, you will start to thin the edge. I usually suggest about .030" for carbon steels and taking extra time on pre-HT sanding.
Why not take the edge to .010" or even .005"?? ...well, that starts a new problem. The decarb can penetrate several thousandths of an inch, which could lead to an edge that is all decarb. Also, at those thin sections, the steel moves easier as the phase transforms, and can cause warp and a "bacon twist" edge. Cracks are also more likely in a thin edge due to the great stress during the martensite transformation.
IMHO, every blade should have about .003-.005" removed from each side post-HT. Most of that is in the final sanding, but even if you want a 220 grit finish, take that off each side. It exposes much better steel and removes all decarb. We regularly see people with a dark splotch on the blade that won't buff away...it is almost always a spot of deeper decarb they left behind because, "Everything looked good after HT."
