Only if you want to see how cuts will interact with each other. You can draw things where the kerf will be wider than the space between nearby lines (especially with intricate artwork). Having the line defined as the kerf width (for ones that will be no-offset cuts) or twice the kerf (for cuts you’ll make with an inside or outside offset) will show where the material will actually have the cutouts. That’s what will show you where tight angles and other fine features may end up being burned out by another cut.
Regardless of the defined stroke width, the CAM path calculations are made using the center of the stroke. So if you’re doing an offset path, it will back the torch away from the center of the stroke by 1/2 the width of the kerf. That should let the actual material cut to just kiss the line. For a no-offset cut, it lays the torch center right on top of the center of the stroke and you end up with a cut where 1/2 the kerf width is on either side of the line and your part size is reduced from the design as a result.
I do my designs using a hairline stroke and the Geometric Bounding Box setting so the dimensions in the drawings are true. Then if I’m doing tight artwork, I’ll bump the stroke width to the kerf or double-kerf just to see if I’m going to have any issues with overlapping cut channels (CTRL-A to select all and then set the stroke thickness to the kerf…CTRL-Z to undo before I close the project so it’s back to normal).