Inspired by Backy in another thread. I think she was referring to a actual full meal/menu item ordered to go. For clarity I'm referring to partial meals or "leftovers."
Do you ever request them?
If you do, do you (or somebody) actually eat the food? How often do they get thown away?
Under what circumstances will you (or not) ask for one?
Do you find it annoying/in poor taste when others at your table do?
etc. etc. etc.
Me personally: I never used to, but I now find myself asking under certain circumstances. First of all I need to know my dining companions very well. I would never do it with casual business colleagues or at a business dinner in general. Second, it needs to be something I genuinely think I'd enjoy eating later. That is I'm going straight home (vs. it sitting in and stinkling up a car for a couple of hours) and can properly refrigerate it and it will reheat well.
In fact I've found myself at lunch ordering extra meals "to go" to be reheated as dinner for myself or myself and friends, depending on schedules. Obviously somethings reheat better than others.
One pet peeve. I have a business associate that I end up in group meals with quite a bit. He always skips desert but orders one to go that he says he gives to his daughter later in the evening. Now I'm sure he scores points as the All-Star Dad but I think that it is poor form to deliberately order something you aren't going to eat when someone else is picking up the check. If you feel bad about missing dinner with the family, stop at the ice cream shop on the way home and get her a treat.