Settable fluids comprising particle-size distribution-adjusting agents, and methods of using such settable fluids in subterranean and surface applications are provided. In certain exemplary embodiments, the settable fluid comprises a cement, a set retarder, and a particle-size distribution-adjusting agent. Exemplary methods include, but are not limited to, methods of drilling with the settable fluids, methods of cementing with the settable fluids, and methods of using a settable fluid to displace another fluid from a well bore in a subterranean formation.