My wife and I have sex three times a week: Tuesday nights, Friday nights, and Sunday mornings. I know, not very spontaneous - in fact, the exact opposite of spontaneous, lol - but the scheduling makes it happen, and we both want it to happen. We have been doing it this way for ~25 years, and while it isn't a perfect system, it's worked for us. I appreciate the consistency, and also the GGG attitude we bring to each other's needs. Our sessions still run 45 min to 2 hours, and we still have a lot of fun w/each other during that time.
We discovered early in our relationship that my wife's sex drive wasn't quite as strong as my own, or maybe she was just more easily sated. My size (girth) also made it difficult fo her to have penetrative sex on consecutive days. She found she needed a day off between sessions. Once we had kids (now teens), it was just a lot easier to schedule things.
Again, we've been doing this for about 25 years. While I might have wished for more frequent sex earlier in the relationship, I am grateful that we have maintained what we have, and our pace has not slowed. From talking with friends, I think I am luckier than many of them.