Question about the tube in the Vincent PHO-700

I had one of these for evaluation.  The tube is in the circuit.  However, I was not a fan of their approach.  Essentially, this is a Vincent PHO-8 with a tube added to the end of the circuitry.  It's not like the tube replaces any solid state parts; the tube is there I assume for coloration purposes.  It is also worth noting that the moving coil stage is about 2 steps away from being awful.  The difference between the 700 and a 701 is the 701 has a usb out.

Lots of cats enjoy the 701. But there are also difference in both stages as the new 701 has switches for the MC. And I've heard that the   tube in the window can be rolled as its in the circuit.

If you remove the tube and the preamp still works then you will know that it is not part of the circuit. Why would the tube be controlled with the dimmer switch?  It seems that the tube is there just for looks!