But it also helps in reducing the load on your servers when, e.g., instead of 300+ login attempts per minute on your mail ports, you get 20 because the IP gets

But it also helps in reducing the load on your servers when, e.g., instead of 300+ login attempts per minute on your mail ports, you get 20 because the IP gets banned for a day after 2 failures. Or, instead of nginx spending 90% of its time sending out 404s for the various PHP and MySQL holes I do not have installed, it can spend 10% of its time instead. Particularly on my small server, fail2ban is the difference between "usable" and "on the edge of falling over".