The concept is the slower everyone is flying, the more aircraft you can fit in a small airspace. The lower you fly, lower tas, slower flight. UAE FIR is like SZR at peak hour. Sure, you can do 120km/h at 5am, but at 5pm, everyone is doing 40 and there are a lot more cars fit into any given stretch of road
Flying slower and lower burns less fuel compared to flying to a holding pattern at M.84 and then holding for 20 minutes, whilst taking the same amount of time. It works pretty good. We don't hold that much in DXB anymore, certainly not for the hour plus we used to arriving before midnight.