EDM of deep ribs is hindered by carbon deposited onto the tool electrode. this carbon changes the electrical tranference and inhibits the sparking. the jump (peck) can remove the carbon. the time spent NOT cutting becomes a problem. the high speed jump gets best of both worlds. more work is done with a cleaner tool. the peck simply spends less time in the peck due to the velocity. Modern plastic molds require ribs, take apart any plastic case and look. mills cannot create deep narrow ribs.