Even after you have configured your Sharing Setup control panel, no one, not even the Guest account, can gain access to your system until you have configured folders or disks to be shared. File sharing won't happen until you give access to something to be shared--either folder or disk.
The appearance of a shared folder changes. When a folder has been configured to be shared, there will be network cables pictured at the bottom of the folder. When another user is using the folder, faces appear on the folder.
Once a folder has been shared, no folder above it in the disk hierarchy, or the disk itself, can be shared. If you try to do this, a dialog box will tell you the item could not be shared.
For example, if you share a folder on a hard disk, and then try to share the hard disk, the system will complain. You must turn off sharing on the folder before the system will allow you to mark the entire disk for sharing.
However, the opposite is not true. If folder A contains folder B, and folder A is shared, you may still share folder B. This enables you to set different permissions on folder B from those on folder A.