Ellen Lupton – D. I. Y. Design It Yourself lecture (2006, University of Arizona)
“[..] one of the things we learn about typographic rules, that you learn the rules and you understand the why behind them, and once in a while you find that it’s OK to brake them, but you brake them from a position of knowledge, not ignorance.”
I think we can all agree that this is true not just for typography, but all other aspects of design and usability, not just letters (with font faces, heights, wights, so on) but also the actual text / paragraphs (with alignment, line – letter or paragraph spacing and so on) or other spacing, dividing, aligning, sizing of composition elements that make symmetry and/or actual sense by contrasting with height or weight on a greed or with color.
Such rules imply indeed symmetry and/or consistence and avoidance of clutter of elements (not just physical elements like paragraphs of graphic elements but also clutter of font types or colors. Why are these bad? The purpose for avoiding these is one of the main and most important objectives in a good design, that is clarity and ease of accessibility of the actual information that the content brings.
Here is Ellen Lupton’s “Thinking With Type” dedicated site, and below is the lecture from which I extracted the quote.