The movie way of showing tension between couples is when one person (usually the guy) gets kicked out to the couch. American culture (I can’t speak for other parts of the world) jokes about being banished to the couch if you’re at odds with your spouse.
The idea is that sleeping together = closeness = togetherness = commitment to spending all your days and nights together. Sleeping apart = independence = fractured/distant relationship in public perception.
That said, sleeping preferences are a sacred thing, and torturing yourself into sleeplessness and subsequent tiredness during the day is never a good idea. I’m sure tons of couples need their space—a larger bed, separate beds, separate rooms…to me it seems unusual for a couple to do that, but it’s not a good way to judge a relationship.