The checkpoints are similar files as the original notebooks but are only updated on a manual save. The original notebooks are updated with autosave and when manually saving (thanks @Thomas K).
The question to you is if you want to share your manual saves with your collaborators. I prefer not to share those because git already provides the functionality to go back to an older version.
Also, I use https://www.gitignore.io/ to create .gitignore files and according to them the checkpoints are temporary data.