You know - I've never really used the symbolic notation for setting permissions, but you made it super simple. Thanks priyanka yadav for the guide.
Think of a scenario in which a particular user is not a member of group created by you but still you want to give some read or write access, how can you do it without making user a member of group, here ACL helps us to do this trick.
And even ACLs, I haven't made use of them at all. But good to know.