A couple with one television
Two people, one set, watched together almost every evening. The overlap count is one, because there is never a second screen running. They both follow the same football, so a single line-up covers both of them, and nothing in the house is likely to change for years. This household buys one line on the longest term they are comfortable with and puts the end date in a shared calendar, and that is the entire decision. The one thing worth checking first is whether either of them has a channel they would miss, because that is the only question that can make a second line-up necessary.