In Windows you can use it to add information of your file or add-in into the Windows register, you can use Regedit.exe to view this info in the register in Windows.

The good news is that SaveSetting, GetSetting and DeleteSetting are all working on a Mac. But there is no register on a Mac where can you find the information that you save ?. On a Mac it will store this information in .plist file, the name of the plist file is the name that you use as first argument in SaveSetting

You find it here /Users/UserName/Library/Group Containers/UBF8T346G9.Office/Profile Settings/

Note: Library is a hidden folder on your Mac, this is how to open it in Finder :

Basic example to save for example the version number that is in a worksheet cell :

Old bug: The only thing I notice that with the GetSetting default argument you can't use an empty string to load if there is no value saved. As a workaround I use "?" instead of "" in a few of my add-ins, but it looks like they fix it in Mac Office 365 now so there is no problem anymore.