Is Audit Trail an additional cost per Full user? Is it a system requirement for each full user? I am curious if other organizations have this enabled and what benefit it provides.
I don't know the answers to your first questions, but can give you insights to how we use it. I am the LF Administrator for our ORG and I keep an eye on Quality Control. Any time I spot an entry that doesn't look like it followed the patterns we expected it to, I can access a track record of everything that happened to that entry from day one to current day. I can see who did it and usually what they did. Who named it, who moved it, who deleted it, who templated it, etc. etc. Sometimes, this clues me in to the fact that Workflow did it, after which I can check out which workflow and why it did what it did in case I can alter the workflow to make it work better next time. What I most often find is that it was our newer employees that did it and I can then go to the user and provide them with more training.
Audit Trail is usually costs a percentage of all full users you have.
We use Audit Trail a lot. In most cases it is when a manager or someone has a question about who changed a template field on a document, deleted a document, or deleted pages from a document. Audit Trail can let you know all of that and more.