Yes ... when the required impedance of the transmitter is 50 ohms. However, in a multi-band doublet with 600 ohm open feedline, there is a need to have a variable match capability to assure the transmitter is satisfied. The impedance of the doublet may have wildly different impedance than 50 ohms, either inductive or capacitive in nature and in fact may not be resonant. However, it will radiate fine regardless of any arbitrarily set impedance, like 50 ohms. There is nothing magical about 50 ohms. It depends on the overall system in question. Like a 134" doublet fed with 600 ohm feeder, the impedances the tuner will "see" will be anywhere from ~20 to 3000 ohms +/- some amount of reactance. And I am not sure what you mean by a "standing wave antenna system". I know some automatic ATU and SWR meter manufacturers have used that strange terminology in their manuals, but I still don't know what it means or what it refers to.