Never, really.
I went to my parents house for almost every Thanksgiving and all Christmases until I married DH. Then we celebrated with both our families by trading Thanksgiving and Christmas back and forth. So one year Thanksgiving was with DH’s family and Christmas with mine. Then, the next year we would switch. We hosted or traveled, taking turns. Some years we traveled for both, some we hosted for both, other years we hosted for one and traveled for the other.
Now all four of our parents are gone and we still get together with family. I5 has evolved to be Thanksgiving with DH’s sister and Christmas with mine. Again, we trade off hosting, for the most part.