Atmasphere brought up a reason for having some loading with stages sensitive to RFI. I helped set up a table for someone with a Hovland preamp. We had problems with noise that turned out to be RFI. The factory "default" loading for the Hovland turned out to be 100k (essentially no loading). The unit had to be opened up to find this out and to make a change. Adding some loading cured the RFI problem.
A cartridge manufacturer, I believe Jonathan Carr of Lyra, mentioned another possible reason that loading might help. He noted that the response peak of modern cartridges are so high in frequency that loading should have minimal effect on audible frequency response. However, he speculated that some phonostages or linestages might be incapable of handling the signal level of the ultrasonic peak of cartridges, in which case, some loading might help in taming such peaks.
A cartridge manufacturer, I believe Jonathan Carr of Lyra, mentioned another possible reason that loading might help. He noted that the response peak of modern cartridges are so high in frequency that loading should have minimal effect on audible frequency response. However, he speculated that some phonostages or linestages might be incapable of handling the signal level of the ultrasonic peak of cartridges, in which case, some loading might help in taming such peaks.