Why might a sample be resuspended and centrifuged again after an initial separation?

A sample is resuspended and centrifuged again after an initial separation primarily to achieve a more complete purification of the desired materials.1

During the initial centrifugation, a partial separation of suspended particles of different sizes can be achieved by stopping the process once the larger particles have packed into the sediment, while many smaller particles remain suspended in the fluid. If the goal is to isolate both the larger and smaller particles, the surface fluid containing the smaller particles is drawn off, and the remaining sediment is resuspended in a suitable liquid. This mixture is then centrifuged again to effect further separation of the components.1