I went 15 years without one, but would get up overnight to check the Egg. If the charcoal settles, ash can collect and snuff out the fire. When I was working nights, this happened twice and I vowed never again. For the $150+ meat I lost in those two, it only cost me that to get a temp controller about 5 yrs ago.
I'm now a dealer for the three big brands and the one I sell the most of is the cheapest and simplest. You turn the dial to the temp you want, and that's it. There are other units that offer ramp up/down functions, alarms, WiFi, etc.......none of which I ever use on the BGE. I use those functions on my Rebel 23, but that because it takes forever to change the temp on that monster. If you have a Maverick or other remote thermometer, you already have most of those extra functions covered anyway.
It's a lot easier to explain all this over the phone, so send me an email/IM with your phone number if you want to chat.