One advantage of the DNS01 approach is that you can also order certificates for standby instances behind a load balancer, all fronted by the same domain name. S

One advantage of the DNS01 approach is that you can also order certificates for standby instances behind a load balancer, all fronted by the same domain name. Since the standbys are not serving traffic, you can't get an HTTP01 challenge/response through, but you can still do so with DNS01 and get a certificate delivered to that machine, so that it's always ready to serve TLS in the event of a failover.