Genomics can help to delineate the boundaries of ethnicities. This is useful because people of different races in a shared/neighbouring ethnic regions such as around the Mediterranean often share far more genetic similarity than they do with people of the same race in northern Europe or sub-Saharan Africa. The concept of race has always first and foremost served privileged groups and oppressed groups, often along ethnic lines, but not always. A great example is how pasty ass Irish people were once not considered "white". The genetic argument is typically cherry-picked to reinforce these power structures.