I was amazed how many people hooked up their water and sewer for one night. Then had to fight with unhooking and putting it away the next morning in cold and near darkness. And sometimes rain! It seemed crazy to me. You've got several days worth of fresh and sewer water storage, it's no big deal to use them for a day or two. Be brave!
Maybe that's what they'd been doing, and it was time to dump the tanks, and they left them hooked up overnight so they could do laundry in the evening.
In fact, chances are, if I'm in an RV park for only one night, it's pretty much just so I can dump the tanks and do laundry. So if I'm the one-night-hookup person you see, it's likely that it's because I'm coming off a couple of weeks of no hookups at all, and not that I have to have them at all times.