In my family the gathering is almost always at my mother's home since forever ago. My sister, sister-in-law, brother and I prepare the meal, set the table and serve the food. Sister, sister-in-law and I clear the table, do the dishes and clean up afterwards, brother sits with the others, aunts, uncles, cousins, and other guests. We work very well as a team, other guests always comment on how seamlessly we work together as they watch from the dining room.
One cousin in particular, and her husband, used to visit from out of the country at various times of the year, Christmas, Thanksgiving, Easter, the usual family gathering times and they would always comment on our "dance in the kitchen" and what a good team we were.
One year I drove 1200 km to go visit the above cousin and her husband at their home and after dinner, I got up and began helping my cousin by clearing the table and putting away food, because that's the way I was raised, family helps. Her husband was extremely annoyed with me, told me that his mother would never allow non-family members in her kitchen and that it was "common". I was dumbstruck and finished putting away the dish I was holding and went and sat down. (I also left the next day, I was so embarassed.)
I had no idea that I was so out of line in their home, but since then, I ask if I can help and don't just assume that it's welcome.