What is the point of geoblocking IP addresses with cisco firepower or a similar service if the firewall would block the request anyway? For example, We only do business in the USA but see source IP's from Russia/Netherlands etc hitting the firewall all the time. Sometimes the IP's are part of a botnet/wannacry affiliated or other malicious sources. The firewall quickly denies these packets but what Im trying to figure out what good would geoblocking do if the IP's are being blocked by the firewall's implicit deny rule anyway?
You may have services that you provide to the US that you do not want, or are not allowed to, provide to certain geographies. Examples: software downloads (particularly with Crypto) to countries on the federal crypto exclusion list. Video distribution to countries where you are not licensed to serve those copyrighted videos.
If your web services are not used by certain countries, and those countries have a substantial quantity of attackers, by all means geoblock those countries. This is very helpful against "script kiddies" and random scans.
You are correct that blocking something that is already blocked has no purpose. Geoblocking is an additional block selectively preventing access to services you permit from some countries.
The protection geoblocking provides is imperfect. Attackers in country-A are only inconvenienced by a direct geo block and may use a jump host in country-B. Some people also use country-specific VPNs to bypass geographic video distribution restrictions. But every inconvenience you add may cause the attacker to focus elsewhere.