They are widely used in electronics today in the form of 8-lead integrated circuits and are used as switches with four inputs, three outputs, and a control.
A voltage applied to all four inputs will be seen on all three outputs when the control is "on" and generally the inputs are wired together and the outputs are wired together. By rapidly switching the control on and off you can effectively change the output voltage.
The real values are that there is almost no leakage current when off and they switch very fast.
In most electronics, they are used as protection. Most electronics today has many different power rails (5v, 3.3v, 1v, etc.) and a MOSFET (or multiple in parallel) is off, until a control chip turns them on and if a problem is discovered, they are turned off to prevent damage or fire. Once switched on or off, they stay that way until a new contol happens. In fact, you can turn one on or off on the benchtop connected to nothing using the voltage from an ohmmeter!
In a motorcycle rectifier/regulator, they can be used as a part of the rectifier and/or part of the regulator. I don't have the Tri-Spark schematic, but based on the waveform of the output, I think it uses them as a rectifier and regulator combined. They produce slightly more output power than the older types and almost no battery drain when the bike is off - MUCH less than any other system I've tested.
