When showing the author in an article, that author can be linked to its associated contact profile (when the Contact content plugin is enabled). This plugin allows that link to open a contact view created by Trombinoscope Contacts Pro instead.
The last contact associated with the author (user) is the one that shows.
The default view option is useful if you need the authors to open under a certain menu item.
For instance, you could have a page showing a grid of teachers (Trombinoscope grid view) and when clicked the teacher's (contact) profile would open. On your site, you could also have a page with posts of teachers and you would like the author's link to open the teacher's profile under the Trombinoscope grid menu item.
On a multilingual site, as long as menu items in different languages are associated with each other properly, no matter which language you chose for the default view, the plugin will create the correct link for the current language (if you select a default view in Spanish for instance and if visitors are browsing your English portion of the site, the profile opened will be the English one, as long as you have associated the English and Spanish menu items properly).