The admin checkboxes control mostly what SITE commands a FTP client can issue to the server. These SITE commands have specific features they do.
VERSION - gets you the current server version.
USERS - lists currently connected sessions.
KICK (session id) - use the USERS SITE command to get the session list.
KICKBAN (session id) - use the USERS SITE command to get the session list.
PASS (password) - allows you to change your password.
ZIP - makes all dir listings end everything with a .zip extension so a GUI client can understand the list and download an item as if it were a .zip file.
DOT - shows or hides items starting with a dot as the first character.
QUIT - kills the CrushFTP server as soon as this user logs out.
CHMOD 777 (filename) - changes the Unix permissions on a file.
CHOWN (user) (filename) - changes the unix owner on a file.
CHGRP (user) (filename) - changes the unix owner on a file.
Allow passwords to be emailed - controls if the login page of the WebInterface will email this user their password.
Allow Web Proxy / Adhoc proxy - controls if a built in proxy mode CrushFTP has can be used by this user, and if they can generate their own proxy connections.
Remote Administration - allows this user to connect with another copy of CrushFTP to do remote administration of the server. They get a full unrestricted GUI just like you are using.