We use this feature extensively at $dayjob.

Imagine you have some task you are working on, and you wish to share your progress with people in bite sized chunks that they can review one at a time, but you also don’t want to wait for their reviews before you continue working on your task.

Using a stacked set of PRs you can continue producing new work, which depends on the work you’ve already completed, without waiting for the work you’ve already completed to be merged, and without putting all your work into one large PR.

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Gigachad an hour ago | parent [-]

I've always done this by just creating new PRs that are based on the branch of the old one. Maybe this is a UI improvement?

	▲	steveklabnik 23 minutes ago \| parent [-]
		Yes, you can do that, but there's lots of things about it that are awkward. This makes it a more first-class feature.