Originally Posted by
Mark Bolton
Bitmap trace will rarely if ever leave you with single line vectors. As David said, it will detect the thickness in the line and generate a vector on either side of the line (which is normal.. "the line" is actually its own entity)
Depending on the complexity of the drawing you may find that you have more post editing using bitmap trace than if you just loft lines around the sketch manually. On very complex traces it can save you a bit of time but even then you will more than likely still have a heavy amount of post processing/node editing after a bitmap trace. Where bitmap trace often shines is with thick line drawing that have well defined edges and very little noise in the source bitmap. Anything beyond that you will have a pretty hefty amount of cleanup.
Only you can decide if your faster getting some initial vectors from bitmap trace and then editing or just vectorizing the job from scratch. Perhaps not wise to weave another hefty variable into the process but you can often times come out ahead using a free program like Inkscape to generate clean vectors to then import into Vcarve for final tweak.