wp_wfFileMods contains the changelog of files in your server. The plugin check plugins and themes folders and compare those files with the originals in the wordpress official repositories. This is done by keeping a detailed track of all the files in your wordpress installation.
My tables for this aren't so big, so I assume you probably have a huge WordPress installation, with plenty of plugins, themes and/or lots of images uploaded.
In the other hand, did you optimize the tables of your database sometimes? Because deleted data in the database generate gaps of garbage that can make grow a database and even make it underperform.