Almost all LDAP schemas use an attribute (cn) for the group name that is specified to be case insensitive. Unless you are connecting to a LDAP server that uses a different search attribute than the defaults you should leave this as Case insensitive.

Recommendations:

• If your group search filter is blank or contains cn={0} then select Case insensitive.
• Otherwise consult the LDAP schema of your LDAP server to determine the correct selection, with Case insensitive being the best choice for the lazy.