Very wide use.

I just finished a large healthcare web site that uses page anchors.

Page anchors are recommended by one of the (many) federal web accessibility guidelines. This is so that people with limited motion or poor motor control, or visual impairments don’t have to scroll to find what they’re looking for on a page.

It’s also how the “Skip to content” links work, which is Accessibility 101.

Sorry, I’m not at work or on a computer so I can’t link to a reference.

Here's a reference for "Skip to content" for those who have never bothered to make their web sites usable for people who aren't 20-somethings in perfect health (Google):

https://webaim.org/techniques/skipnav/