Here’s another of those “someone asked an interesting question on the Illustrator subreddit” posts. They wanted to know how to automatically fill a shape with a pattern brush that looked like embroidery stitches.
This is one of those things that seems like it should be super simple to set up as a live effect in Illustrator but turns out to be impossible. But a little abuse of some third-party plugins makes it doable! Astute’s WidthScribe lets you make a bunch of lines with the Width Stamp effect, and then you can use the Appearance palette to apply whatever kind of stroke you’d like to those lines – here I’m using a custom brush, but you could do whatever your image needs.

Then, go to the Appearance palette and add a new stroke to the whole Width Stamp group. Not to the individual paths inside it.
embroidery stamp.ai – 152k, requires the Astute suite.