Can verify, still a thing. There is even a fun saying that goes with it.

"Normalize until it hurts, denormalize until it works."

Yes, especially in business intelligence / data warehousing. Here is an excellent resource if you're interested in this sort of thing: https://www.amazon.com/Data-Warehouse-Toolkit-Complete-Dimen...

It's a term used frequently in NoSQL land, to explain a key difference to people coming from SQL. In SQL land, normalizing your data is still the canonical thing to do, and I don't recall anyone in academia officially talking about denormalizing ever having its place...but in industry, the realities of use cases and performance have meant its usage. But I don't know that it's a standard tool given out to graduating software devs and DBAs.

The link I posted above is a common SQL land usage. Dimensional modeling in a star schema is very widely used in BI projects.

There's actually two competing philosophies on data warehousing (Inmon and Kimball), but I've only ever used Kimball's method, which favors denormalization.

http://www.computerweekly.com/tip/Inmon-vs-Kimball-Which-app...

Of course they do, that's why there are the Normal Forms. Since like the 1970s people have been talking about this stuff. It's actual maths.

Yes, and almost always used as pre-emptive optimization that didn't need to be done. Often times even making things slower because the person doing it didn't understand what they were doing, they just heard "denormalizing makes it fast".