I don't know about the OP's use case, but we have received requests from our clients to know exactly when users start working on documents and when they finish working on them.

Some managers want to know when their employees actually start processing a document after they have been assigned it during a workflow step. The idea is to gain deeper insight into the business process by having access to document-level reports. For example, there can be a lot of value in knowing that invoice A took 2 minutes and 14 seconds for the clerk to process (from the moment they opened the document to the moment they closed it), whereas invoice B took 1 minute and 29 seconds.

Then they want to combine these document-level reports into higher-level reports to be able to say, for instance, invoices from Vendor A always take the longest to process, so we should probably find out why. These types of "deep insights" are currently not possible without making things very complicated for line workers (e.g. open a document, then mark a metadata field as "started working on this", save changes, work on the document, then change the field to "finished working on this", save changes again, etc.).