It's a hotel-by-hotel thing. I've booked a 5 night stay before and then taken a side trip that turned into a two-night stay away from the hotel, and got an email from the GM indicating that housekeeping had reported that I hadn't stayed in my room and did I need them to check me out. So I said no, and that I would ck out at the end of my reservation and that was the end of that.

If you're concerned about it, simply advise the front desk that you plan on being in and out and might stay with local friends but not to check out out, etc.

O/H