The usecase is for people who want a single-user/small instance or those who are completely new to selfhosting. I'm pretty sure SMTP works if you configure an external one (like Mailgun or SendGrid) which is what most people do (including me) since the SMTP config is done via lemmy.hjson (or in the case of Lemmy-Easy-Deploy, the config.env file). IMO, the only thing that makes Lemmy-Easy-Deploy worse for production use is Caddy which performs worse than nginx in some benchmarks. But I don't think it's that bad.

But if you don't want to use Lemmy-Easy-Deploy, then here's my own documentation on how I installed Lemmy on my server. It's different from the standard Lemmy docker or ansible install where I use nginx natively instead of containerized as this fixes my certbot issues. I'm not an expert on any of this but this is how I got it running.