And to add to the summary, in order to map to your computer, another user would have to know:
1) your computer name
2) The fact that C$ exists (this is a hidden admin share)
3) A user name and password for your local pc.
A properly set up network will have groups set up by area, function, etc so that ONLY those that have a need get access to their area, group, etc. All others either won't know about any other shares or will get an error message when they try to get into these other shares.
And finally shared folders on a server are good esp. when it comes to backing up files/folders. Makes restoring easier if files are kept centrally located. Most network admins don't back up users pc's.