John Mueller from Google has advised site owners to restrict blocking Googlebot if they plan to block traffic from an entire country. Many site owners consider blocking individual countries during times when they receive problematic traffic. However, Mueller seems to be against this idea and prefers avoiding the same. Read more at www.searchenginejournal.com
Looking from an SEO perspective, it is preferable not to block Googlebot from crawling a website since it majorly crawls sites from the US. Further, blocking traffic from the US will result in causing more problems.
Instead, make sure that the individual countries you are blocking are not the ones that Googlebot is crawling your site from. By doing a reverse DNS lookup, you can easily find out about the Googlebot traffic.
Finally, it is at the discretion of the site owners to block traffic from a whole country or not.