I spent 8 years working in hotels in GR. We had a similar service, Park n' Fly.
Typically it's a pretty good deal. You pay for one night at the hotel, plus pre-pay for a designated number of days that your vehicle will be parked. Typically much cheaper than parking at the airport, and any good hotel will offer complimentary shuttle service to the airport and pick you up when you get back.
I can say this much. We never kept track of who was a park n' fly guest, nor how many days their vehicle was parked. If they were gone 10 extra days that they didn't pay for, we'd have never thought twice of it.