We've all come across this at some point: a beautiful-looking design... with ridiculously illegible type. Now don't get me wrong—there are defiantly some great designs that specifically use type in artistically illegible way. However, when it comes to signage and communicating vital information, legibility trumps prettiness.
Don't choose a typeface just because it's pretty; choose a typeface because it works hard and delivers. As a designer, it's a constant concern of mine to consider how the type will hold up under different conditions in the real world. What distance will it be read at? What are the lighting conditions? Is there enough contrast between the type and background? What's the viewing angle? Is it digital or printed (or something else)?How readable and legible it is for the key demographic (and other users)? Is the user likely to have some sort of visual impairment? What age are they? Are they moving while reading the text? How fast?
Here's an old article, but a good read nonetheless: Read Typography and the Aging Eye