'...... use two voices. '
Prob some do use two. Or three? The Roland MT32 has some using 4, just checked this. If you want your results to be useful, you need to check this carefully.
May depend on the architecture, or the 'vintage (and hence the amount of onboard RAM/processing power). Maybe newer kit more likely to be 1:1, while the MT32 (and it's various clones) is fairly old with less sophistication built-in and therefore needed to be 1:4 for the more fancy sounds.
Geoff