please see the Unity documentation  It is mentioned in a lot of the manuals  basically LDAP could either by used for Management of admin users of the GUI/CLI/API  or as directory Service for NFS/CIFS/ftp or to configure multi-protocol user mapping  If you dont know why you want to use it then I suggest to read all of them
need help in configuring ldap for unity 300f. is there any document available other than the CLI guide on the support site?
unity 300F ldap configuration