Typography is all about readability and legibility. While working as a webdesigner, I’ve studied much about this: When your customer asks you to put red Comic Sans MS letters on black background, you need to prove your words with some theoretical studies.

I always fight for using simple readable fonts, black letters on white background.

Many people don’t feel the borders of readability and non-readability, so that is the reason why we see so many examples of awful and ureadable ads.