I worked as a cook for over four years and I did every last bit of work on to-go orders. It provided no extra hassle on either end, and was less of a burden on the waitress. The only reason a waitress should have to do extra work for to-go orders is if the kitchen is not well-organized. When I was a cook, I made all the food, packaged it up, took care of silverware, bagged it up, and put it in the window. All the waitress had to do was fill to-go cups if the customer ordered drinks, and hand the food to the customer. If the customer wanted any extra sauces or dressing or anything, we either had them pre-portioned for the waitress to just toss in the bag, we had packets (ketchup, dressing, steak sauce, etc), or I took care of it.
I understand that this might not be the case in some restaurants, but I made it a point to make the waitress' job as easy as possible.