So, I get the "squash your feature branch into a single commit before merging upstream", but what does doing "git merge main" instead of "git rebase -i main" gi

So, I get the "squash your feature branch into a single commit before merging upstream", but what does doing "git merge main" instead of "git rebase -i main" give you? (Assume I have my global git config to remember conflict resolutions via rerere)