'Controlling' swtich and the 'Companion': I don't understand the concept here.

[skydiverMN]

Howdy all.

Is the 'companion' simply a switch that is controlled by a 'Controlling Switch', and this companion would be wired to control some other item?  Is the reason to use this method to save on occupying an itemID within a channel?

Can you give me an example?
This is me: 

Thanks.

[dave w]

Howdy all.

Is the 'companion' simply a switch that is controlled by a 'Controlling Switch', and this companion would be wired to control some other item?  Is the reason to use this method to save on occupying an itemID within a channel?

Can you give me an example?
This is me: 

Thanks.

You are close on your assumption of the companion switch. The Companion Switch is the "second switch" in a 3-way switch setup in your home. The "main switch" (the switch which has HCUC dials), such as a WS477 actually controls the light fixture and would be used as one of the two 3-way switches. The Companion switch is then used as the second switch. The companion switch sends a signal over the existing three-way wiring, which tells the WS477 to turn ON. The Companion switch is useless by itself and is always used as the second switch in 3-way, or 4-way circuits where X10 is used to control the light. X10 makes Companion switches in either button style or "Decora" paddle style to match the fixture controlling switch.