The arrows represent dependencies. For example, if you create a function A that calls a function B in a pull request: 1. We'll render function A as a diff on the top part of the canvas 2. We'll render function B as a diff on the bottom part of the canvas And we'll draw an arrow from A to B, to represent that A is calling B

In this way, you can more easily understand the relationships between different parts of what someone is editing. We hope that this reduces the amount of mental modeling or mapping someone has to do during code review!