Let's say I'm working on a feature branch, and end up realizing I should really be opening two PRs because this one PR is going to be two hard to review. It's m

Let's say I'm working on a feature branch, and end up realizing I should really be opening two PRs because this one PR is going to be two hard to review. It's much more difficult to reorganize commits on your feature branch if you have merge commits from the main branch mixed in with your changes. If there was merge conflict resolution along the way as well - good luck making sense of things. Merge commits 'lock' you in to the commits you've made so far.