I have an Optimus laptop. MSI. Card 1 Intel, card 2 Nvidia. I NEVER use card 2 Nvidia. Reason: it heats up like a mofo. Within just a few mins., 180F. The laptop has a turbo fan option built in just for this.
Randomly, depending on what I am doing, my light comes on indicating the GPU is active ( Nvidia ). It makes me SO nervous! Sometimes just when an update comes in that isnt even anything special. Sometimes when I am installing something. It only started doing this since the fresh install. Previous kernels, drivers, ect., never did this on the original install last year even leading up to the exact kernel/drivers I have now..
Before anyone asks there is no way to disable the card in the BIOS. Also, I do not use the proprietary Nvidia driver on this OS. I'm using Nouveau.
I wouldn't even care except for the over-heating associated with this Nvidia card. There has also been a few occasions where the GPU came on and stayed on and I had to reboot twice praying that Intel would be called and not Nvidia. During the boot up process, the light switches back and forth, even when the desktop loads. Then the light finally goes white and I breathe a sigh of relief.
Synopsis is: I do not want to use Nvidia, and really I dont want to blacklist it. Just behave and when I want you... be there.

Edited to Solved: The more I thought about it, the more I suspected it was a driver/xorg issue. Inxi was reporting nouveau failed and desktop started not loading. I installed Nvidia drivers, bumblebee, and primus, and voila, back to normal.

It makes me SO nervous!

@Ubulindy I can certainly understand what you mean.