[SAI_Peregrinus]

Github's interface is a big part of the issue (only for those using Github, of course).

Say you branch off of master, make some changes, and make a PR. Call this branch A.

Then you want to make a new branch, that depends on branch A. Call this branch B. The PR for branch A is still waiting to merge when you finish with branch B.

If you make a PR to merge branch B to master, you get a diff showing both PRs worth of changes. That's annoying to review.

If you make a PR to merge branch B to branch A, you get the correct diff for B. Huzzah! But if branch A's PR then merges, Github deletes the branch B PR and any comments/review. You have to remember to retarget branch B PR to master, then merge branch A.