I was setting up pull/pull systems for a couple years before I ever heard the term Ackerman and all my planes flew very well. Even after learning what it was and how it worked I didn't worry much about it until I started getting into precision planes and there set up. As a sport pilot it mattered to me not at all, if I had the slack in the cables I never worried about it. Then I started precision flying with pattern and IMAC planes. Incorrect Ackerman didn't show up on my pattern planes due to the speed flown but I finally started to notice it on IMAC type of planes and flying. That's when I started taking the time to set the Ackerman correctly. Any good 3-D or free style pilot will notice it instantly. When you pull your rudder to the slack side there is a delay in the rudder movement and authority or speed until the slack line starts taking control again. I agree with CG, as beginners it isn't something to worry about but as beginners it is something you can start incorporating in your planes now so you learn how it's done and get in the habit of setting up your pull/pull systems correctly. Due to servo placement and how the lines are run inside the plane you sometimes just can't get all the slack out but you can usually get them close. I got along quite well before I ever heard of Ackerman but I do strive for perfection in my aircraft set up. Don't always get it but I try hard. No reason to ever loose sleep over it though but now is a good time to start learning how to set up your planes as well as you can.
I have friends here on RCU that dwell on the subject, I try but tend to not over think it.