What happens if there are both a prefix and a suffix?
Like Magnus Gabriel de la Gardie d. ä.
You can enter both, to enter suffix, you click the combobox to have suffix, and the entry field updates.
It is a way to save space only, the alternative is just adding a line under there to show suffix and title as real fields, but I believe those are not that common. The window title shows the full name of the person as per the display settings