Imagine you are putting an expression jack on a Fuzz....
1) Controls Clean Blend in all settings, which in-the-end is pretty subtle
2) Controls a Filter Sweep, which can add a neat wah-like sound in some settings, and does nothing in others.
3) Controls Drive Level of entire pedal in all settings, allowing trem-like effects.
Not a poll, because I'm more concerned with people's well considered opinions rather than their vote.
Three jacks, or a switch...
D.Don