Imagine you have a parent-record and multiple child records. Using this new combined-text field; you can summarize the unique-values from a text-field from ALL of the child-records and let them be displayed in the Parent-Record. The summary field display will separate each child-record entry in a group, similar to multi-select text values. In some cases, that format can be hard to view/display; so I often have to build an additional formula-text field using the function ToText() on the summarized-field to display the content properly, separated by semi-colons.
If you have the same value from that child-field more than once; it will only display once in the combined text summary field.