It doesn't seem like there would be that many reasons to turn your car into a wifi hotspot, but consumers now demands to be connected to the web on all their devices all the time. There's wifi on planes and wifi in trains and now, with GM, there's wifi in cars. Surprisingly, the in-car wifi works the best right now.
GM loaned me a car for the weekend so I could drive around Vermont eating cheese, drinking cider, and pointing at leaves. We were those annoying New Yorkers who people in Vermont treat with a quiet disdain despite the fact that, as far as I can tell, their entire Birkenstocks-and-Subarus economy is built on the $6 tiny leave-shaped glasses of syrup we all buy at The Vermont Country Store as we make our way out of the state.
It was a new Impala which, in addition to being a perfectly nice car, also comes with a built-in 4G LTE wifi hotspot that can connect up to ten devices. This car only seats five so the idea that I'd need to connect seven devices seemed comical until I actually tallied the number of wifi-equipped devices the four of us had casually brought with us (Eight, which equals three MacBook Airs, four iPhones, and an iPad).
We spent a few hours in the car so there was plenty of time to check out if the 4G LTE was actually worth using — most vehicles equipped with 3G I've tested provide a barely passible connection just good enough to check email.
The system is fairly easy to use as all any of us had to do was find the network, which in this case was "impala30hotspot" and type in the password (which the car was able to remind us via a hands-free command).
Unlike your phone, which also probably has 4G LTE capability, the antenna for the system is mounted on the roof of the vehicle and is larger and more powerful than what you have in your pocket. It uses AT&T's network so you're going to have a similar experience in terms of getting service, although I found the car had a better chance at getting a signal than I did with my phone.
I also found the connection was stronger and more consistent than what I've experienced on a plane or in my many attempts to use WiFI when traveling on Amtrak. Granted, the passengers in our car weren't fighting with some dude in business class trying to download "Ass Buffet 2: Caesar's Revenge" but we did test Netflix streaming and it worked without any pause while cruising down the Interstate at around 65 mph.
Some of the areas we went were fairly remote so the speed varied greatly, ranging from sub-1.0 mbps to a high of nearly 15 mbps, but it was mostly a consistent 4-6 mbps, which is fine for most uses.
So is it worth it? If you need a reliable internet connection in your car then it's a gimme, especially if you use your car for business. But the average person? Probably not. At the cheapest, you're paying $5 a month for 200 mb as an OnStar subscriber, with 5 GB going for $50, in which case I assume you're living or working out of your car (or both!).
If you don't need this service but have one of the many cars from GM equipped with the system you can always opt-in on an ad-hoc basis if you need to turn your car into a wifi hotspot in an emergency — having lost power in a hurricane more than once I do wish I'd have had a car equipped with both a 120 volt outlet and a hotspot.
It's an interesting bet for GM and they're clearly at the forefront of this technology (Audi is next, offering it in the new A3) if this is what we all decide we want. However, this is a risk that our phones will become better at working as nodes for cell tower-based web and the idea of a car equipped with wifi will seem as hilarious as those cars that offer "30 GB hard drives" for all of your music.