[From "Rapid Development" by Steve McConnell]
"Padding [a schedule] is a bad idea because it gives the customers the wrong idea about why schedules are imprecise. Padding says, 'I don't think our estimates are very good.' An estimation range with periodic refinements says, 'The estimates are good, but it's not possible for an estimate to be precise at this stage in the project. It will become more precise as we go along.' "