In most cases, a maker can manage to get the channel cut with other means.
If I were to burn it in, I would only use this method on a wood handle. I have done it but prefer other means.
When I do burn the tang in, I make a slightly undersized mock tang of mild steel and use that instead of the actual knife tang. There needs to be a guide hole drilled. Once the entrance hole is cut/drilled and enlarged, I heat only the tip of the mock tang and push it in and remove it quickly. If you heat the whole length of the mock tang, you will cook the wood around the entrance.
I use this means sometimes as a starting method and finish the process of fitting using broaches so as to remove the scorched and charred lining.
As with any method, this takes practice. Poorly done will certainly ruin or weaken the wood.
I believe this method is borrowed from old practices where handles were fit to tapered tang tools such as wood chisels and draw knives.