i haven't really seen the need for any type of external temp controller yet.
i'd like one, but there always is some higher prioritiy item on my wants list.
It's definitely not necessary, especially with a BGE. I got through a bunch of overnight cooks without one. Just the normal remote Polder thing with an alarm so you get waken up if there are problems.
Where it comes in handy is that I can cook while I am at work, so I can do long cooks during the week. Plus calling your coworker in your office and showing them that you are controlling your smoker from the office is almost worth the price. Somehow the beer thing still seems cooler to everyone though.
Plus I could mash on BGE which, now that it occurred to me, I kinda want to do.