[skj]

Here's a screenshot of some side-by-side diff action: https://fr.atlassian.com/wac/software/fisheye/overview/scree...

Basically, it let's you look at the old code, or look at the new code, or see how they're different, all at the same time.

Inline diffs (github-style) require you to keep a context as you scan through code, and it makes it harder to keep everything in your head.