Extended ACLs are easier to manipulate. When working on a router, if you have an extended ACL, then you can remove access-list entries (ACEs) from the middle of the list - something you cannot do with the standard ACLs. Further, you can remove ACEs from the middle and add ACEs in the middle. You can even resequence the whole ACL so that the line numbers are consistent.
The use of named extended ACLs is basically to have a better description on what the ACL is for.
To know if an ACL is being used, some of the things you can do are:
1. Execute the command "show running-config | inc access-group". This will show you if there are any access-group statements in your configuration. If there are, then it means your ACL has been applied somewhere. You will then need to check the configuration and see where it is applied.
2. Check the line vty configurations and see if you are using ACLs there to define which IPs can remote to your router.
3. Check your SNMP setting and see if you have an ACL restricting which IPs can SNMP to the router.
4. Check route-maps and see if you are using an ACL there (if you have route-maps, then you must be having an ACL associated there defining the criteria for that router-map).
5. And last but not the least, you can do a "show access-list " and see if any of the hitcounts alongside the ACEs is incrementing. This is not a decisive test but if an ACL is being actively used while you are checking, then you should be able to see the hitcount increment.
(My 2-bits).
