This is an intermediate light switch. Do you need an intermediate light switch?
You only need it if you have three or more light switches controlling one light. In which case the middle one(s) need to be intermediate.
The two end ones need to be two way light switches.
Click here to read more details on what an intermediate switch is, and when you may need one.
With this two gang intermediate switch it is possible to wire either or both switches as intermediate switches or two way switches. Please see the details on how to wire a Retrotouch intermediate switch for for more details.