I don't use fabric softener. However, in an effort to prevent winter motor fuel problems, I use cold weather fuel additives. When that temp. gets below 0, I want my car to run, or I could freeze to death out on the road.
What is the benefit of additives? I have never used them except in my windshield solution. One winter I made the mistake of turning on my wipers to "clean" the windows in the middle of winter. Immediately the solution froze and I was unable to see out of the windows. I was unaware that gas freezes as well.
It depends on what "additive" we're talking about. There are different ones, that do different things. I keep seeing some that claim to "clean your engine". I guess you'd have to dismantle your engine ... or run a camera probe ... to see if they actually work.
B.H.Wilson 