There is often a need for different reasons to deny any access to the site to any users of certain countries. For example with DDoS attacks, a large amount of spam, BruteForce Attacks, or the unwanted traffic comes from addresses of a particular country.
The GEOIP Block function not only blocks unwanted traffic but also significantly reduces the load on the server thereby making your site faster and more optimized. Google has repeatedly stated the importance of the downloading speed of the site for its ranking in the search engines.
Imagine a situation where a DDOS attack has started on your site or someone simply sorts through the passwords to the admin panel of your site. The loading pages speed is significantly reduced and potential visitors see a white window or a 404 error when they try to open your site. Therefore 9 out of 10 visitors will simply close your page and go to the page of competitors thereby spoiling your Bounce Rate. And even if you don’t believe that Google takes the speed of page loading into account when determining your position in search SERP it has been known for a long time that the behavioral factor is considered by all search engines.