As many have already said it is a nice to have not a need to have. I have had one for a couple of years and have really enjoyed cooking with it.
I did have to make a few adjustments as I was figuring out how to cook with it. Keep in mind that the Guru does it's job best when it is in complete control of the air flow. For me the key to success is to have all air sealed off except the fan at the bottom and the top vent. I will take a few pieces of foil and fold them up to make a gasket of sorts for the seam between the two bottom pieces of the WSM (eliminates potential air leaks). This ensures that the guru can do it's thing regardless of the weather conditions.
Stumps Elite 7, 22 & 18 WSMs, La Caja China, Bubba Keg, Weber Kettle, 180 Brisket Club