Why would anyone want no rules? what is the point of an empty RuleSet?

The main purpose of this RuleSet is to allow the individual enabling of rules

Create a new file (something like custom-rules.yaml) and add the following YAML to it:

extends: [[spectral:oas, off]]

This creates a ruleset that extends ‘no’ rules. You can find this ruleset in the rulesets/examples directory, and it’s named norules-ruleset.yaml

Now you can enable rules individually:

extends: [[spectral:oas, off]]
  operation-operationId: true
  description-duplication: true

Now you can run any vacuum command that supports a ruleset.

lint with ruleset

There is a specific-ruleset available as an example.