Manage App Set Up Storage Page Explained

From "Manage Application" > "Setup" > "Storage", you can choose whether all file storage will be used from the same location (App Level), or each site can set their own file storage location (Site Level).

If you choose "App level", it means all sites will use the same file storage location, and you can click on the "File Storage Location" drop down menu to select which storage you want to use.

If different site managers use different file storage service, you can set it to "Site level", and site managers will choose the file storage from their "Manage Site" > "Storage" settings.