Accor is the only other global operator I know of besides Hilton that has made booking Day Rooms very easy on its website.
You may want to book a day room for a long transit or if you need private space during a day (or perhaps even loyalty qualification purposes).
The most logical need for day rooms is close to airports and preferably with hotels attached to a terminal.
You can get the Heathrow Sofitel Terminal 5 for 135 GBP for a stay from 8 AM until 6 PM.
You are eligible for all status-related benefits, such as upgrades and lounge access.
Conclusion
I tend to book a day room if I have a long transit during the daytime, as staying inside a lounge or two gets really boring after a few hours.
These may work in your favor if you arrive on an early morning flight to your destination and want to ensure that you have a room available when you arrive at the hotel (8 AM early check-in is likely not often available).