If you use a webmail application for work you will more often need functionality related to business instead of private life. One example is an addressbook, where your contacts can have various properties.
In Roundcube addressbook you can select from many properties both with “work” or “home” label, but the default is private life. Starting from version 1.5 you will be able to just switch to “work mode” for faster access to work-related properties.
This is simply improving the experience of finding professional information about your contacts. Work-related properties will be displayed first. The contact creation/editing form will also display some fields, that normally are hidden, by default, like organization, department and job title.