The definitions are stored in the wp_options table with the option_name of “GOTMLS_definitions_blob” and currently use about 191KB of space, or around 518KB if you also have the Core File Definition (included with automatic updates). With each new definition added it might increase the definition size by anywhere from 200 bytes to 1,500 bytes, though many of the updates are only changes to existing definition and not additions of new ones, so those can be very small or even sometime smaller than the former definition (in which case the update will reduce the overall size of the definitions.
In short, these definition updates take up an significant amount of space in your database. The GOTMLS_definitions_blob will be automatically deleted from your database when you deactivate the plugin, and you can always download the latest definitions from within the plugin if you reinstall it.