I guess what I am really curious about is whether, in a marriage, if you eliminate one big source of conflict (e.g., money), whether other sources of conflict are reduced as well. I could imagine that if you are constantly fighting about money with your spouse, your interest in physical intimacy is lessened. I was speaking a bit tongue in cheek about sex being inexpensive entertainment...as others point out, nine months after the act there can be a big shock to finances!
But also, as someone else pointed out, I am implicitly assuming that both partners are on board with the Mustachian vibe. That is probably true of many (most?) followers of Mustachian, but not all. And I suppose that a divergence between partners in that area could lead to friction in other areas, including in the physical relationship.