one of Let's Encrypt key principles is, as you know, it is
Free: Anyone who owns a domain name can use Let’s Encrypt to obtain a trusted certificate at zero cost.
I read and understand this key principle in a more private sense, meaning, it is free for private/ non-commercial use.
But I am asking myself, what would be fair use principals of/ for commercial/ business/ company use-cases and furthermore for municipal, federal and/ or state administrations world wide?
Let’s Encrypt has rate limits in place that limit things like how many certificates you can get per domain per week, etc. As long as you stay within these rate limits and don’t try to work around them in some abusive way, you should be fine.