and in direct answer to your question:
100v line stuff is used to provide systems where the speakers will be a long way apart. there are various reasons for this but basically each speaker has a transformer in it to drive the cones. this means that there is less effect from voltage drop on the cable runs but leads to a loss of signal quality and a fairly drastic drop in ‘loudness’. it also means you are not running a high current along wires in a public area/outdoors/in thwe rain
‘normal’ PA systems use lower voltages but higher currents. this allows greater power to be delivered over shorter differences negating the need to tone the voltage down at the cabinet
personally i’m more of a ‘whacking great big amp’ kinda guy but have had some experience with 100v line stuff