The fGDB files are archived data, data we receive regularly from other agencies or third parties that are used to update our enterprise GDB, temporary files when working on new feature sets or classes as modifying enterprise GDB schemas can be a pain during normal business hours, a few datasets we just do not want to add to our enterprise deployment, quick onetime projects, etc. We still do edit some of these files but only by a handful of people.
We also have the a separate folder on the share for shapefiles. However, all our shapefiles are immediately imported into various fGDB or our enterprise GDB as feature classes for use internally. Well, they are suppose to be anyway. Working with shapefiles as part of your normal workflow is not their intended function.
To answer your question, I would say 70-80% of our editing is performed in the enterprise environment. The remaining portion is using fGDBs.