I have seen Pre tensioned ball screws in large CNC machines, Also many where one end is fixed in preloaded angular contact bearings While the other is allowed to float in to allow for changes in temperature. The floating setup may be a less difficult setup to use, particularly if the frame is lightweight. If you pre tension you are imposing a substantial load on the frame, It would have to be stiff or it may be deflected out of alignment by the preloading stress, and the deflection would be likely to vary with temperature.