When I was first using chef -- and didn't quite get the paradigm -- it was really easy to fallback to a lot of native ruby. i.e. "I dont want to run these resources in certain contexts, let me just wrap them in an if statement." Which ended up creating a bit of a mess over time, and broke some of chef's functionality.

By using yaml ansible basically forces you to be purely declarative, which I found to be a boon, especially once other engineers who similarly didn't initially get the declarative paradigm started on working in the codebase.