Whenever you make an important save, you should use the "Post to Project" button to add a revision to the timeline. You can then describe what you did in that revision, and attach an audio preview to it.
You can Post to Project from either the project's timeline or the Splice app (the button will appear on the app after you save).
If your project is to private with no collaborators
This is the default state of any project. Use posting to remember your important milestones in the project.
If your project is set to private, with collaborators
You can use posting to share updated revisions with collaborators. Once you post, all collaborators will be notified via email about the update, and can then open the revision and post back their own.