Saving artwork and metadata directly into media folders will put them in a place where they can be easily edited and help reduce the size of the server's data folder.
Extracting chapter images will allow clients to display graphical scene selection menus. The process can be cpu-intensive and on average will require 1-2GB of space. It runs as a nightly scheduled task at 4am, although this is configurable in the scheduled tasks area of the Dashboard once the wizard is completed.