What does the "Copy Mix" function do?

The "Copy Mix" function is available for Main mix and aux mixes. Sometimes it can make sense to just copy a mix to another. You can also copy a mix to several aux mixes at once (if you want everybody to hear the same mix...). The copy function will not work for matrix mixes and subgroups, also not for effect mixes.

A quote from the UC Surface Reference Manual, section 2.2 Copy Mix:

Copying the current mix allows you to quickly set up multiple mixes based on the settings you’ve already completed.

1. To copy a mix to any other mix, press the Copy Mix button.
2. Click on the desired destination mix(es).
3. Click Paste to paste the mix or click Cancel to stop the operation.