Normally you will see only asterisk when you are checking SNMP community string in your ASA firewall as below.
To uncover the string, you can use below command.
So that you can check your SNMP Community String and can do some other task which related with SNMP.
This is useful for checking your ASA Firewall which setup by other Engineer or the time you forgot your string.
This command not only for SNMP Community String but also for ntp pre-shared-key , vpn pre-shared-key, etc.
Have a good time.
(Be knowledgeable, pass it on then)