FWIW, I do not think it would be wise to try to sit in a seat that another passenger is trying to save for his wife / partner, etc., regardless of what the official policy says.
The entire flight would be rather uncomfortable for me. Then again, I like to get along with people.
I think for most flights this would not be an issue. Only on a highly crowded flight where one partner is early and one partner is way late could this be an issue.