There is no doubt that you want your holiday to start of as relaxed as can be. People often find airports stressful, if you have an early flight then an airport hotel may be the best way to start your holiday. Wake up, have breakfast, either in your room or the hotel restaurant and then head over tot he airport terminal.
Most airport hotels offer airport shuttles as part of the price or increasingly as more are built on airport sites you can simply walk from your room through to the departure terminal itself.
Gatwick and Manchester both offer hotels where you can walk through in under 5 minutes. The perfect choice. Increasingly it is also cheaper to book a hotel with parking than just parking. As odd as it may seem you can almost get the hotel stay for free or the price of your breakfast, so its worth considering.