This would allow any element to be styled like any other element through interactions. The value and potential is almost infinite so it is hard to describe.
The most common instance for me would be setting hidden values to elements outside of the child/sibling class limitation. Some other useful scenarios from recent projects would include:
Allowing for all other CSS changes not covered through the default provided set with interactions
Resolving the inability to create scalable blog categorisation due to the inability in setting conditional visibility on multi references by allowing a CSS class against the parent of collections
Not having to create multiple interactions for elements that need click to current and hover interactions requiring any CSS outside of form webkit. In other words, custom form elements.
Stacking scroll, hover or click interaction on top of each other in an easy way.
Ability for more experience Webflow users to create templates or repeatable patterns that beginners could purchase or use that includes interactions they would not have to manipulate or understand to utilise (this one is hard to explain but comes from giving a lot fo training to people starting out with Webflow)
Other cool stuff...