I suspect I recently disabled it. It is under the "Importing and Tagging" section and the implication I took was that this meant updating library tags when the file tags had changed...
I always import via shell integration menus, and often from a root folder, eg the artist, rather than specific albums, thus often running the import process of multiple albums, some of which will already be imported. And because my girlfriend uses the same library there is a chance she could have written tags to "my" previously imported files - I disabled this option thinking it would stop my library updating from her changes. But clearly this "Tagging" option affects save tags to files and tags from files and has nothing to do with importing, even though it's under the same heading?
I therefore think it would be helpful to separate the two entries to remove this confusion?
Mark