Ugh, there’s some parts of YAML I love, but ultimately it’s a terrible format. It’s just too easy to confuse people. At least it has comments though. It’s so dumb that JSON doesn’t officially have comments. I’ve often parsed “JSON” as YAML entirely for comments, without using a single other YAML feature.
YAML also supports not quoting your strings. Seems great at first, but it gets weird of you want a string that looks like a different type. IIRC, there’s even a major version difference in the handling of this case! I can’t remember the details, but I once had a bug happen because of this.
Performance wise, both YAML and JSON suck. They’re fine for a config file that you just read on startup, but if you’re doing a ton of processing, it will quickly show the performance hit. Binary formats work far better (for a generic one, protobuffers has good tooling and library support while being blazing fast).