Let&#x27;s Encrypt gives encouraging automation as a reason why they choose 90 days:<p><i>They encourage automation, which is absolutely essential for ease-of-use. If we’re going to move the entire Web to HTTPS, we can’t continue to expect system administrators to manually handle renewals. Once issuance and renewal are automated, shorter lifetimes won’t be any less convenience than longer ones.</i><p><a href="https:&#x2F;&#x2F;letsencrypt.org&#x2F;2015&#x2F;11&#x2F;09&#x2F;why-90-days.html" rel="nofollow">https:&#x2F;&#x2F;letsencrypt.org&#x2F;2015&#x2F;11&#x2F;09&#x2F;why-90-days.html</a>