Revisions allow you to track differences between multiple versions of your content, and revert back to older versions.
I have made a start on drafting a manual for absolute beginners - it has barely got to grips with OpenMx as yet, but I will attach it as far as it has got, and would welcome comments (and some help in the places where I have indicated that I have got stuck).
SMB attachment updated on 7th March
Further update on 10th March, but can't add it as it exceeds disk quota. Email firstname.lastname@example.org if you would like a copy.