In a similar vein to shifting around the number of points per night required (usually around a holiday time frame), there are also the instances of individual resorts creating 'minimum stay' requirements (effectively blocking single night points reservations). We have experienced this ourselves within the past couple of years at MVC properties on HHI that required a 2 or even 3 night stay to make a points reservation during certain 'high-demand' dates. This is never a published restriction on the MVC website, but with some creative date searches you could see changes in availability confirming the existence of these 'resort imposed restrictions'. For example, the website shows availability for a certain date range on a Thursday, Friday, and Saturday. However, when you attempt to search for just a Friday using the same date as the proposed 3 day reservation, it shows nothing available.
While not a big deal to many folks, I suspect (unless they either live near a desired single-night destination or use single night stays incident to other travel), the ability to make single-night reservations was promoted as an 'ownership perk' of DC points (and is definitely being manipulated at the resort level in some locations).