Let's compare 2 approaches to delivering commits A, B, C.

Single PR with commits A, B, C: You must merge all commits or no commits. If you don't approve of all the commits, then none of the commits are approved.

3 stacked PRs: I approve PR A and B, and request changes on PR C. The developer of this stack is on vacation. We can incrementally deliver value by merging PRs A and B since those particular changes are blocking some other engineer's work, and we can wait until dev is back to fix PR C.