Installing new rotors without ever measuring and documenting the condition of the old rotor is like playing chicken with a comeback. Sooner rather than later, you will find a vehicle that will not be magically fixed by a new set of rotors. In fact, the new rotors may cause even more problems and lead to an unsatisfied customer.
Back in the day, a non-directional rotor finish was the method used to solve a common problem that occurred on bench brake lathes. If the cross-feed speed on some lathes was too fast, the rotor became the record and the pads became the needle that followed the grooves in the record. This would cause a clicking noise as the pads moved in the caliper. Today, a non-directional or post-lathe surfacing process still serves the same purpose, but it also helps in the bedding of some friction formulations.