Is the priority of rules / expression settings different for different controls?

I sometimes feel lost as to whether I should use the Expression setting for a control or add a fresh rule.

Is there any kind of guide or set of recommendations as to which is best for what control?

It would be a great help, and save me from much head-scratching when I see rules not working as planned or expected.

It would be great to know which is best to use for different controls.