To Premult or not to Premult

Now, I've known that 3D elements rendered out of Maya need to unpremultiplied before compositing, but I still wasn't sure when exactly I needed to do it.

I stumbled onto a document at work today that explains the rule:

1. Unpremult before any color correction, and pre-mult after
   
2. There's no need to unpremult before filtering options like blur because these operations should affect the alpha channel
   

Example:

Without un-premultiplying:

With: 

It's subtle, but the white 1-pixel halo around the green character's arm is gone.