We do use it. I like being able to put in what time we expect to arrive, mostly because we generally arrive very late (midnight to 2:00 a.m.) and it makes me feel better to know they see we are still coming!
Also, using Magical Express, means much of the time we arrive along with many other people so its nice to cut down on the wait as much as possible.
I remember one trip using it and walking right up, getting my packet and being on my way in just a few minutes, vs. the line that was probably at least 30 minutes long. Of course other times, those late arrivals in particular, the whole lobby has been deserted so it didn't matter or save much time.