It depends on which two elements if the planetary you are holding together in the lock position as to how much drag can be allowed in the unlocked position. Anytime a sprague is engaged to stop counter rotation of an element a clutch pack needs to be engaged. Once the clutch is disengaged and the frictions and steels are free to rotate essentially together but not in direct contact with one another there is virtually no wear since the clutch bits are barely separated and lubricated by the transmission fluid. If the one way clutch is dragging during free wheel you risk dragging the frictions or steels and either accelerating the wear on those pieces or raising the heat load to possibly unacceptable levels in the gearbox from unnecessary friction. Modern gearboxes live precariosly close to the bleeding edge as it is. It doesn't take much degradation from component wear to turn the box into scrapmetal.

Yes, Coward... three frequencies... I may have them... the Key!!