A Plus for Plus/Minus
The plus minus system is designed to be a more accurate way to assess your abilities. If you got an A-, it's because you did A- work. It is designed to separate the students abilities more accurately so not everyone graduates with honors.
A lot of students respond with "Why isn't there an A+, if there is an A-? I will answer the question with another question. Why should there be? By getting the A-, you are only proving that you did not even do A quality work. Therefore, the +/- system rewards you by helping your gpa when you should have gotten a B.
Now take a look at some college where every student gets an A in every class simply for breathing. It looks like their college is so good at teaching, when in reality it just means that's it's ridiculously easy.
So when you go to get your next job in the near future, do you want your employer to say "Oh you went to kent state where everyone gets A's just for breathing, maybe I should hire this Akron U. guy", or do you want him/her to say "Oh wow, an honors student from KSU, he must work really hard"?