Diazo rules for Mosaic sitelayout

What diazo rules do you use with Mosaic site layout?

I suppose having as few rules as possible is the best (and move things around in Mosaic instead)

Any examples available ?
Also: is there any use case for setting 'Mosaic' in the 'Theme Base' settings?

Take a look at the Castle CMS Theme.

Does that mean that you skip rules and 'html' file, or is the index.html fallback / default ?

With that approach you don't have to use diazo anymore, but you can still if you want to, e.g. to adjust some content html where you can't use jbot. I think I remember @jensens talked about using mosaic site layouts in a customer project. Maybe he can add some insights.