Unless you are connecting to another Air Asia flight at the LCCT, I can assure you the luxury coaches are way more comfortable and it brings you from city centre to city centre (or almost).
With some planning, you could select a coach company that drops you off near (or at) the hotel you are staying. With the Air Asia flight, apart from having to check-in at least an hour before departure, you also need to take a bus from LCCT to Sentral (if you are not taking a taxi), and from there a taxi to your hotel.
Its like being able to get to your destination with a direct flight (or bus ride) but opting for flights (and/or buses) with 2 or 3 transits instead. Dont think Air Asia has any Frequent Flyer programme, so the possibility of the poster doing a mileage run is out. It just doesnt make any sense at all ...