> Think view-on-view-on-view (there's a BigCo policy against them materialising data..), and where the filter is applied in the last step. The stuff of horrors, but something I've seen in more-than-one-BigCo.

That sounds wonderful (really). I was contracting for a BigCo where they materialised things all the time, and they would regularly end up running queries over multiple materialisations from different points in time, which invariably means that you always get wrong answers. I very much wished to put a stop to use of any materilised views, but didn't have the buy-in to make the policy.