According to the author of the book of Joshua, this verse tells us about the cities given to the Levite priests for them to live in, so they could be close to the people and help them with God's teachings. It's like giving special homes to helpers so they can take care of everyone nicely.
Joshua 21:35: Dimnah with her suburbs, Nahalal with her suburbs; four cities.
These verses include additional cities for the tribe of Gad, which some manuscripts omit, suggesting a discrepancy in the allotment list.
Joshua 21:36-37: And out of the tribe of Reuben, Bezer with her suburbs, and Jahazah with her suburbs,