This is pretty straightfoward- this would sort out a lot of existing problems-

1. It gives the ability to restore just a part of a site ( restore to a new project, then use cross-site copy & paste to pick the elements you want ), including assets like site-wide code, etc. 

2. It minimizes the unnecessary reset of the CollectionID's and ItemIDs, and consequently the breakdown of all Zaps & integrations. 

3. It gives the ability to compare two different versions of the site side-by-side in client meetings. 

However, if the site is based on a purchased template, then this other wishlist item needs to be considered as well;

Allow the ability to clone paid-template projects, without paying again for the template (until hosted).
https://wishlist.webflow.com/ideas/WEBFLOW-I-1531