I've heard they are good for prototyping things where you need to change APIs and spin up new stuff easily. It might be better than using a service where you're basically required to have devops.

That said, you can also just spin up a VPS and use systemd to manage a service at small scale. There are also other PaaS solutions in addition to "serverless/lambda".

I've heard some horror stories about "lambda" pricing as well, so I'd make sure to read into that before becoming too dependent.