If I trace over the pencil lines exactly, it won't look as lively as it would if I only use the sketch layer as a very loose guideline. If I trace the pencil lines perfectly the drawing will look weird and stilted. So when I do a pencil layer, it needs to be very light, and I need to hardly be able to see it at all, otherwise I'll rely on it too much instead of letting the ink layer be its own thing.
I have a very loose, go with the flow style of drawing, so I try to avoid sketch layers if I can. Otherwise the drawing looses its life.