When on a tour in a foreign country, it is always much cheaper to take the bus or train instead of the taxi when going home from the hotel to the airport (and vice versa). Last month when we were in Osaka, Japan, we were lucky because the hotel was a stone’s throw away from the train station. It was no sweat to take the train instead of the expensive taxi. But last week in Hongkong, I had a difficult time carrying our baggage from the hotel to the train station in going home from the hotel to the airport. I had to admit to my wife that I was very tired and my hands were aching. It took so many rest period before we finally reached the train platform. So we agreed that next time we go back to Hongkong, we might as well book in another hotel that is near the train station or just get a taxi for convenience.
Airport bound taxicabs are always dearer than other conveyance. If I travel alone, I never take an airport taxi. But the problem is luggage at times. Due to heavy luggage we have to take the pre-paid taxis as it becomes impossible to come out of Airport with such heavy loads to avail bus or train. Airports are generally in the remote parts of any city. So, the availability of bus or trains are sparse at times.
Considering how exhausting the trip can be and the fact that you're carrying heavy luggage it's quite a tough task to get a taxi since most Airports are generally in the remote parts of cities as moondebi stated, so it's better to call for a taxi before hand to save time and effort.
I tried that idea once in South Korea. I looked massively silly and some older Korean had to mock me. The bottom line is that it's too difficult to haul around luggage and who wants the strange looks etc.? In that case, while it might be a way to save money, a better bargain is to simply plan ahead and assume you will absolutely need a taxi, preferably one which gives a good deal.