Originally Posted by
MSPeconomist
If you're dropping the last night, change your departure date at check in if the hotel doesn't charge a fee for leaving early, although even so the rule usually is that there's a charge of $25-75 for leaving earlier than the departure date that was verified at check in.
Is this always the case? Very often you can cancel your reservation until the day before so I would suppose that if you had a 4 night reservation and change it to a 3 night reservation at check-in they shouldn't charge you.
I do however agree that it's more polite to share this information with the hotel from the moment that you know it, instead of waiting to announce it until check-in.