My take is that, it's okay to get as many multiple helpings as you want, as long as you leave enough time in between to allow others to get food as well. I think one helping is appropriate for the first go-around, although a large helping is acceptable if there is obviously more than enough of the food item for everybody and you're not doing it for *every* food. For example, if there's a cake that had 50 slices, and 20 people are at the event, you take one slice to start with. Maybe not everybody takes a slice at all, so when you are finished your slice, there are about 35 slices left. So you take another. Then you chat for a bit, and later you go back and there are still 20 slices left. You can take another. When you finish, there are still tons left... I mean, at a certain point, it just seems like, if people really wanted that cake and hadn't had enough yet in the time that it took you to have 3-4 helpings, spaced out (not chowing down and then popping back up, but eating at a normal pace and perhaps waiting a little while in between), then they'd have already gotten it. Nearing the end of the party, when most people are done eating and are doing other activities, or people are getting ready to go home, I think it's fine to finish off anything that hasn't been finished already, even if it means eating a lot more than a normal helping. Unless it's an item that is obviously the kind of thing that would be distributed to take home or that the host would really want (a birthday cake, etc.).
