I use it as "insurance" when I have something that looks like it will really be a problem. I was taking some steel fittings out of a used aluminum head, that promised to be a real problem. I hit them with a regular penetrant several times over a couple of days, then heated the head up in my oven. I took the head out of the oven, and hit the fitting with this stuff and it came right out. Did this stuff do it? I dunno, but I got the fittings out with no damage. I think its the combination of care, time, and multiple methods that make it work. Like "mhsprecher" says, it's expensive, so I save it for special cases like this.