Back to the kohen separating from his family - why must he separate? Beyond the parallels we have already discussed, the concern is what if the kohen gadol's wife were possibly impure, because of a question pertaining to menstruation. Also, what about the risk of becoming impure because of contact with a dead body? But that kind of impurity will be overridden by the needs of the community. It's also less common of a risk than niddah Impurity, especially for a kohen who is careful about such things.