Knitting bag vs. project bag

[pbs]

What goes in a project bag vs. a knitting bag? I guess what I'm asking is: does a project bag just hold your yarn, needles, and your knitting item. And then a knitting bag holds all your accessories? I'm trying to decide what size/kind of bag to purchase?
Has anyone ever used the GoKnit pouch with the drawstring? It has a loop inside to feed your yarn through without with the whole ball having to be in your lap. Just looking for some input....