Alchemy is one of those VST instruments that has macro controls.
You assign a couple of midi knobs to those eight macro knob controls and x/y pads, and pick and choose in the VST instrument what those macro controls do.
This is a more advanced form of managing controls.
I imagine some users will want to have these macro controls of Reaper displayed as parameter controls (those optional knobs on the TCP & MCP). Thus you get instant visual feedback without having to open a plugin GUI as well.
Great idea IMHO.