I thought we should start with this one - its a hot topic and a pretty cool feature. We have had the concept of revision roll back in Vault Professional with items for some time now, but alas, never for files.
This meant every time "someone" (not you) made a mistake by changing file state (or more likely changed state as instructed, prior to a change of heart, again not by you) and automatically bumping the file revision, you were stuck with a new revision of the file you could not get rid of.
Pretty much your only options here were to document that the revision was made in error or delete the file and re-add it with the correct revision thereby losing your history.
In 2015 R2 we combined the file and item lifecycle schemes, and turned off roll back for everyone, so we now in 2016 add roll back capabilities to both files and items - and here's how it works:
Say you take your released file and change state - put it into an editable state like work in progress, creating a new file version and bumping the file revision.
You can now go about your work, maybe modify the file (creating more new versions) blissfully unaware your new revision is destined for the junk heap.
When word comes down that the revision is no longer desired, you simply highlight the file, and from the actions menu select "Roll Back Lifecycle State Change"
Vault will prompt you that you are now about to revert to the previous state and all revisions after that point will be deleted.
Select OK and there you have it - the file reverts to Released, the Revision is set back to the previous and any file versions created after the state change are removed - like nothing ever happened.
But what if you have changed multiple files and need to roll back all of them - can I do it in one hit? No, you need to do it one by one - if you have dependencies you need to start at the top level to roll back the parent file then down the structure one by one until all files are at the old revision and versions are cleaned up.
Can I roll back more than one revision? No, roll back can only be done once and is limited to state changes, so if you put into "Work in Progress" and then "In Review" - you cannot roll back to the last released state.
Is that it? Pretty much, that covers the main points, you can read up in help for more details on who can roll back and any other specific limitations.
In the mean time I certainly hope this doesn't inspire a rush to "revise first ask questions later", but its a very handy feature to get you out of a jam and something we've been hearing about for a while, so enjoy!