I have a Voodoo modded SL+ that has these as well. I do not know if they are the same as on the UG since I don't have that module. Having said that, in the Tsunami mod, the center trim pot affects the overall gain of the module. The left trim pot, looking from the front of the module, affects the bass response of the module. At least that's what I notice when I adjust them in my rig. They may be technically adjusting some other things, but at the macro level that is what I hear.
My rig is fairly bass heavy and I can dial in just the right bass and feel with the left pot. I tend to play at bedroom levels so I really like the feel I can get at lower volumes, but also like the fact that I can adjust it for higher volumes as well. I've left the center trim pot alone since I like where it is set. However, I can see dialing back some gain and then hitting with a pedal for a different option and feel too.