Think of it like this.

All the taps basically do is change the impedance of the loudspeaker. So a lower wattage tap results in a higher impedance unit, which means less sound than others with higher wattage (lower impedance) taps.

A 1 watt tap is (for simple math) 5000 ohms, 10 watts is 500 ohms, 100 watts is 50 ohms. Or any combination of taps from any number of loudspeakers.

A 600 watt amp into 8 ohms is a 70V source by itself.

Using the taps to adjust level is the main reason for the various taps.

Let's say you have an airport with all sorts of different ceiling heights. You change the taps accordingly (all on the the same speaker line) for the difference in height (inverse square law) to the listeners ears.

You could use a volume control, BUT IT MUST be a 70V type, NOT an L pad. All a 70V volume control does is to adjust the taps via the switch position. You cannot get it inbetween positions.