The Minimat doesn't have a master volume. It is basically a Volume/Tone amp and if you use the low input and speaker 1, then this is what you have. But as Jeff explained to me when I went for mine, they realised that it sounded great with an overdrive on the front end, and thought that the Fulldrive gave the best sound, but was probably a bit too expensive for people who were buying the Minimat, so they decided to build one in, and make it foot switchable, and include the switch!
At the same time, they realised that it was still very loud to use at home, so they added an attenuator to reduce the output. It is important to realise that this is after the power amp, and is not a master volume.
They also added a DI jack to make it easy to record or send to a bigger amp.