Generally, CV is best for free form or artistic stuff, while Exact Stop is needed when the part must be exactly the shape drawn, no corner rounding off is allowed. You are not likely to get tool marks at the turns, since the stop is extremely brief, but Mach will use the acceleration rate as its tuned to do.
Also the stops are usually at places like sharp corners where you must make a right angle turn.
There are tuning parameters on CV so you can adjust it so it does smooth curves when they are gentle, but does the stop when the angle between moves is sharp.
There was a recent doc put up by Art that defined some of the CV params and their effect. I know it was on the Yahoo group, I think its also here somewhere.