The Sheratons at Heathrow offer competitive parking deals -- often a night in the hotel plus 15 days parking is cheaper than seven days in the airport lot. I don't always need the room, and half the time I check out without even visiting the room (but I always check in and out for stay credit!).

On those occasions when I arrive on an overnight flight from the US, I'll often use the room for 10-15 minutes for a quick shower and change of clothes before checking out.