Its got nothing to do with the receiver. Its to tailor the phono preamp to the cartridge your using as MM and MC all require different gain and impedance settings. MM models may even require different capacitance settings in order to sound their best - very often the lower the better.
So you can see that adjustable Gain, Load and Capacitance settings can be very useful in getting the most of your cartridge vs. a phono stage where these values are fixed. And having them on the front is simply a matter of convenience for the user.
So you can see that adjustable Gain, Load and Capacitance settings can be very useful in getting the most of your cartridge vs. a phono stage where these values are fixed. And having them on the front is simply a matter of convenience for the user.