A big deal is that they get packaged automatically for remote execution. And you can attach them on the command line without touching code, which makes it easy to build pipelines with pluggable functionality - think e.g. switching an LLM provider on the fly.
Metaflow tracks all artifacts and allows you to build dashboards with them, so there’s no need to use MLFlow per se. There’s a Metaflow integration in Weights and Biases, CometML etc, if you want pretty off-the-shelf dashboards