The big knobs act as “amount” controls for the corresponding effect modules — basically, they’ll provide more or less activity for the module. Note that the Boom Shack knob is dual. The center controls Boom level, and the skirt controls Shack level.
Each module also has an On/Off button that enables or disables the module. Click and drag across the buttons to toggle multiple modules on/off in one go.
When you mouse over a big knob, a padlock icon appears. Click it to preserve the corresponding module’s current state even when switching to a different preset. Parameters can still be adjusted manually while in a locked state.