This thread got me curious, so I took a look at it. It seems you can use this function to create multiple variants of (a group of) attributes and show them on a single location in the chaptercard. You can switch between the variants by using an up/down arrow. 

There are many cases where it could be useful to have multiple variants of attributes, for example for design cases, but I think there are better (object based) ways to manage that.

Perhaps, in some cases, this could replace the functionality of a 'List' attribute.