John in NM
I think you guys are both saying the same thing really - it works great when the cut is very light, perhaps halfway between chopping and paring as far as technique goes.
The problem Derek describes comes from too heavy a cut - just as you mention is the drawback. The problem is that the reference surface isn't actually a constraining surface, its more of a guiding one. Too heavy a cut and the waste chip pushes the chisel out of plumb and into the non-waste material. Continue on that path and you'll cut past the line on the other side.