My two usage cases for Let's Encrypt certificates
My first usage case for LE certificates is as the first stop for temporary certificates for test machines at work. I not infrequently need to set up test versions of TLS-based services for various reasons, including testing configuration changes, operating system upgrades, and even whether or not I can make some random idea actually work. All of these cases need real, valid certificates because an ever increasing amount of software refuses to deal with self-signed certificates (at least in any reasonable way). Since it's very unlikely that I'll run a test server for anywhere close to 90 days, various sorts of LE certificate renewal issues are of little or no importance.
LE's rate limits mean that I may not be able to get a certificate from them when I want one (or renew an existing one if I'm about to recycle one of my generic virtual machines to test something else), but this is more than made up by the fact that I can try to get a LE certificate in minutes with absolutely no bureaucracy. If it works, great, I can go on with my real work; if not, either I put this particular project on the back burner for a few days or I get us to buy a commercial certificate and forget about the issue for a year.
(And when I can get a LE certificate for a general host name, I'm good for the next 90 days no matter what I'm doing with the host. Even though it's a little bit ugly, there's usually nothing I'm testing that requires a specific host name, or at least nothing that can't be fixed by hand editing a few configuration files for testing purposes.)
My second usage case is as the regular TLS certificates for my personal site, which is basically the canonical Let's Encrypt situation. Here I'm unlikely to run into rate limits and since I'm the only person getting certificates, I can coordinate with myself if it ever comes up. I do care about certificate renewal working smoothly, but on the other hand there are few enough certificates involved that if something doesn't work I can do things by hand and in an extreme case, even go back to my previous source for free TLS certificates. I'm also willing to run odd software in a custom configuration if it works for me, since I don't have to maintain things across a fleet of machines with co-workers; 'it works here for me' is good enough.
(And, while I care about my personal site, it is not 'production' in the way that work machines are. I can take risks with it that I wouldn't even dream of for work, or simply do things as experiments to see how they pan out. This is partly what Let's Encrypt is for me right now.)
These two usage cases wind up leaving me interested in different Let's Encrypt clients for each of them, but that's once again a subject for another entry.