The “selling point” of dual extruder printers is not just 2-color prints, but the ability to print a separate support material. The right nozzle can be loaded with a filament that acts as scaffolding for the main part, then after is snapped off or even dissolved away.
This print-in-place ball bearing from GCreate is designed to test this. The wispy, translucent material is PVA, which dissolves in warm water, leaving just the red PLA and a working ball bearing with no assembly required.