JMHO, but I don't think they are necessary if you are using a good grade of fuel. I use Chevron with Techron (premium) because if keeps fuel guages functioning and injectors clean. You can buy cheaper, but you get what you pay for. For example, Corvette fuel guages have a bad habit of failing because of cheap fuel. 2-3 tanks of Chevron cleans out the sulpher that fowls the guage sending unit in the tank. (This may hold true as well on a CTS, if they use similar technology on the fuel senders.) If your car is a daily driver, just use good fuel and save your money.
Gas line antifreeze additives are required if you habitually drive around with a low fuel level and park in a heated garage. The heating and cooling cycles promote condensation on the inside of the gas tank. If you keep the fuel level up or park in an unheated area you should have no trouble from that source. That being said, gasoline is sold with a certain level of dissolved water that is not easily removed in the manufacturing and delivery process. Warm fuel directly from the refinery has the most water. As the fuel cools the water settles out. If the fuel becomes cold enough ice crystals will form and will plug filters in both point of sale pumps and the auto itself. To be safe, a little gas line antifreeze can be helpful. On the other hand, some cheap alcohol based products can corrode the heck out of your fuel system. I haven't heard too much bad about HEET gasline antifreeze.
That's my worry, its now very cold here in new england and I do park in a garage at night, its kept at about 50 degree but its been like 30 or lower outside lately.. For the last few days its been in the single digits. So the car is in and out of cold and warm conditions. But I do use Plus or medium grade gas all the time.
I'll probably add a little dry gas just to play it safe. Maybe fuel system cleaner every 10 or 15 thousand miles.
What is added to the fuel at the refinery is a local option and is entirely unregulated except for the areas where certain aditives are required for emissions control. Fuel systems cleaners(Techron) that are added to "Top Tier" gasolines handle varnish and the like but do little when it comes to water. Aviation turbine fuels that have the most stringent requirements for handling and process control require fuel heaters as part of the aircraft fuel system and the addition of anti-ice additives such as "Prist" if you don't want to finish your trip on snowshoes rather than in the confort of your flying machine. That being said, a lot depends on where you are in the fuel chain. The closer you are to the refinery the more likely water is to be a problem.
I suppose if you don't care about your wife and kids being stranded in a life threatening situation it's a non-problem. It's one thing to do dumb things to yourself and quite another to do the same to innocents.
I"ve lived in New Enland all my life. I've driven hundreds of thousands of miles. I've kept my cars in heated (40-50deg) garages. I've kept my cars outside all year as well.
I've never had a fuel line freeze. All I've ever done is kept the fuel topped up, usually never lower than 1/4 tank. About once an oil change I put a bottle of Techron or Redline fuel treatment in the tank. Colder climates my require more agressive strategies, but for weather in southern New Hampshire/northern Mass, I don't think extra steps are necessary.