Roon always attempts to provide a current, accurate view of your files, which is why we scan for changes at startup, and also monitor your storage device for changes with real-time monitoring and periodic re-scanning.
Giving you an accurate and current view of your files was a key design goal for us, since we’ve all had the experience in iTunes where a track appears to be available, but when you click it you get a nasty surprise because the media has been moved or deleted.
Feel free to open a feature request describing how you’d like us to change our storage implementation or to allow the option to disable the initial scan of your storage devices, but to be clear, the the screen you posted above (with the “loading” logo) is not Roon scanning your storage – during this period the database is loading so your Core can start up.
Scanning of your storage happens after that, so I just want to be clear that “make Roon start up faster” and “allow me to disable scanning at startup” are two different requests, and aren’t really related to each other.