You said it, for us the main benefit is that the hotel knows precisely when you arrive and most often early check-in is made available.

2 weeks ago we stayed at Swissotel The Stamford in Singapore (not a luxury property but it offered the best views over the Padang for the Independence anniversary celebrations). With more than 1.000 rooms check-in is supposed to be a disaster, but as we had booked the transfer through their concierge service, check-in was performed in-room and we saved at least 30 minutes queuing.

Quite often top luxury hotels are also the only ones to offer VIP assistance at the airport. With Amankila, Amanjiwo, MO Bangkok, Peninsula HK, we were taken in charge right at the exit of the plane and even with economy tickets we were rushed to premium passengers lines for immigration.

It's part of the experience, even if the price is crazy I would not consider taking a regular taxi and queue for hours.