AAA & Tacacs+ Configuration

Hi All,

Could someone please explain the following Router configuration to me in an nutshell?

These commands are configured on an Company Router and I am wondering if they are all necessary, I would like to understand them in detail and try to eliminate if not needed.

aaa authentication login default group tacacs+ local
aaa authentication enable default group tacacs+ enable
aaa authorization exec default group tacacs+ local

aaa authorization commands 1 default group tacacs+ local
aaa authorization commands 2 default group tacacs+ local
aaa authorization commands 3 default group tacacs+ local
aaa authorization commands 4 default group tacacs+ local
aaa authorization commands 5 default group tacacs+ local
aaa authorization commands 6 default group tacacs+ local
aaa authorization commands 7 default group tacacs+ local
aaa authorization commands 8 default group tacacs+ local
aaa authorization commands 9 default group tacacs+ local
aaa authorization commands 10 default group tacacs+ local
aaa authorization commands 11 default group tacacs+ local
aaa authorization commands 12 default group tacacs+ local
aaa authorization commands 13 default group tacacs+ local
aaa authorization commands 14 default group tacacs+ local
aaa authorization commands 15 default group tacacs+ local

aaa accounting exec default start-stop group tacacs+

aaa accounting commands 1 default start-stop group tacacs+
aaa accounting commands 2 default start-stop group tacacs+
aaa accounting commands 3 default start-stop group tacacs+
aaa accounting commands 4 default start-stop group tacacs+
aaa accounting commands 5 default start-stop group tacacs+
aaa accounting commands 6 default start-stop group tacacs+
aaa accounting commands 7 default start-stop group tacacs+
aaa accounting commands 8 default start-stop group tacacs+
aaa accounting commands 9 default start-stop group tacacs+
aaa accounting commands 10 default start-stop group tacacs+
aaa accounting commands 11 default start-stop group tacacs+
aaa accounting commands 12 default start-stop group tacacs+
aaa accounting commands 13 default start-stop group tacacs+
aaa accounting commands 14 default start-stop group tacacs+
aaa accounting commands 15 default start-stop group tacacs+

Your help is much appreciated.