Locking The Rig Button?

I was checking for locked modules on my KPA, and I noticed that the rig light was the only button lit, when the lock button was held. I also noticed that I could toggle the rig button, effectively locking the rig. I've never noticed this before. Does anyone know what locking the rig button does?

I haven't played around with it. I'll try it tonight. Thought I'd ask what it does before messing with it. It is already locked (lit when the lock button is held) on my KPA.