wp_usermeta wp_usersettings

When a user changes their admin settings; like the screen options, posts per page or moves metaboxes around or ‘hides’ them, it is saved in their user settings.

So if user settings are blank – the user has never tailored their admin environment.

Aside:
(I use this to great advantage in one of my plugins to simplify the backend initially but allow users to ‘grow’. IE – a ‘template’ user can setup how they would like the admin environment to look by closing meta boxes, changing columns displayed etc. Then when a new user is created, i have the template user settings copied over to new user to present a simplified admin backend. The new user can then add back features as they learn more. I love it!)