Two old school drag race chassis fab guys both told me that they, as well as most in that industry, prefer to use strike-arc and no knob or pedal. One showed me his formed copper strap that he uses to do the actual strike on so that it won't mar the chassis or result in tungsten inclusions.
Off-road fab guys are a newer breed. Doesn't surprise me that they prefer a knob or a pedal, but it is not an absolute requirement. If you ever want to start a war in off-road circles ask if weaving or figure-8 is the better wash-weld technique. Quite a thread on that some time ago on RDC.
