Let's say we have a drum rack with a lot of different samples we have used for experimenting with ideas. After we have finished the production phase, there are only a few of those samples that are getting triggered throughout the whole project, making the rest unused and basically taking up space if we want to "Collect all & Save".
Also when we record audio into our project, EVERY recording gets saved. Now that is great when doing productions to have access to all files, at all times. However, when we have finished our production and perhaps want to move ahead for mixing and post-production, having those leftover files in your project can be very tedious when sharing it to a collaborator or saving the project for archiving purposes.
My inspiration for this feature comes from working with an Akai MPC which allows for the possibility to "Purge" unused audio files. It's very handy and keeps the project nice and tidy