Master volume vs Atenuator

[Chorch Cluni]

Hi all.
I guess I know how an atenuator works, so my question is how in real life does the master volume compare?.

I think a master volume pot works like, say, an EQ through the FX loop, so it can lower the level of a maxed out preamp into the power section, right?.

[J M Fahey]

The attenuator is the real thing, it is flat, sends to speaker an attenuated but accurate version of amp output but most important, it preserves power tube distortion which is warm and full.

Master volume does not, power amp works clean contributing little, all distortion you have is preamp distortion, thin and buzzy.

Besides, attenuator keeps power pentode distortion, MV keeps Triode distortion, very different.