The real value in DNA genealogy comes from using your closest matches to confirm your ancestors going back to your great-great-grandparents - which also allows you to find additional cousins.
For example, I have 15 different Ancestry DNA tests among relatives connected to my Jones line. In addition to me, my Dad and my Uncle, we also have tests from first cousins, second cousins and third cousins. All 15 tests match one another. We have 12 of these 15 tests uploaded to Gedmatch, which we use to identify the exact DNA segments that each test has in common with one another. By knowing these segments, we can then search for other tests on Gedmatch who also share these segments.
The practical value of studying these segments is that the shared DNA segments among multiple tests provide important evidence for connections. For example, 9 of my paternal tests who descend from John J. Coates (1815-1867) of Meigs County, Ohio have several DNA segments in common with 2 tests of descendants of Jeremiah Coates (1817-1895) of Gallia County, Ohio. Meigs and Gallia are adjacent on the map. We don't have paper records yet showing a relationship John and Jeremiah, but this DNA evidence pushes us to look for a relationship.