There’s an art to staying over at a friend’s house. You can’t just show up, eat all the food out of their fridge, spread your clothes all over the place, and expect to get an invite back. A host is doing you an absolute solid by letting you sleep on their couch while you’re visiting their city. Do you know how expensive hotels and Airbnbs are? You should at least buy them dinner or write them a «Thank you» note as a token of your gratitude. You should barely be able to tell that there’s a guest staying there based on how much of your stuff takes up the living room. It’s just common courtesy to be as undisruptive as you can possibly be. Of course, you can’t fully be a fly on the wall (someone still needs to let you into the apartment), but you can do your best.