Possible use to hobbyists although never saw a sting at an SPG property before. However, now SPG has merged with Marriott which is a very non-hobby friendly hotel.
Anyway, in addition to 4 pm late checkout, all Gold SPG members *I just got 4 I note* get 4 500 SPG point certificates to give to a hotel employee. These can be used to bribe the front desk for information about possible stings in the hotel. SPG points can be converted to Marriott points on a 3 to 1 ratio so I believe could also be used to bribe Marriott hotel employees for info.Even without Gold membership most hotels will give you at least a few hours late checkout depending on how booked they are for the next night.
Since I am a late night person, I almost always get late checkout in Canada or when on business in the U.S. I always have flights late afternoon. A few times I did have to pay maybe $40 to extend as far as 4pm.
I usually do Priceline bidding for great low rates at nice hotels unless someone else is paying my expenses (often the case for business). Often pay $US45/night for courtyards by Mariott, Novetel, Best Western etc. in Toronto where Expedia etc rate is well over $100. No issue with stings of course in Canada.