We have a list of known robocallers (like CVS, etc) numbers that are legitimate robocalls but are often spoofed by scammers.
If you have the app set to "Blocked" all of these calls will go directly to voicemail.
If you activate this "Identify Known Robocallers" setting then these legitimate robocallers will only be Identifed, and not sent directly to voicemail.
If you have the app set to "Identified" then that extra setting has no affect. All robocalls will be identified.