Think of Ackerman this way:
1. You know that your inside tire turns a tighter circle than your outer tire (just a smaller diameter circle)
2. This means that it needs MORE steering angle than the outside tire. This difference is Ackerman.
How does it affect?
Well, if you have LESS Ackerman, your inside tire will try to push the car OUT since it is steering a wider circle than it wants (picture it - less Ackerman means the inside tire is steering closer to the same as the outside, so a wider circle than it should). You will feel like you have to fight the car to get it to steer.
If you have MORE Ackerman, your inside tire will want to PULL the car IN since it is steering a tighter circle than the desired turn (again picture it - more Ackerman means the inside tire is steering a tighter turn than it should). You will have a very twitchy car.
Ackerman isn't really something to adjust - you want to find the angle whereby both tires can run the ideal diameter. It IS something to recognize, though.
I was handed a car, a while back, that felt unpredictable. Going perfectly straight, it was great. At high speed turns (where the outside was highly loaded and the inside was not) it was somewhat okay, but felt on a knife-edge. As it slowed down (inside got some load) it would GRAB like a MUTHA and I felt like I had to fight it. . . Turns out the steering rack had a ton of spacers on it and the Ackerman was way over. . . something like 3-4 degrees over what it should have been. . . fixed that and it was predictable again.