If you use your Mac professionally, you most likely also work with fonts.
Fonts are essential for designs and professional print.
And if corrupt, they can cause issues, even crash applications upon launch. Or change your output.
One of the best articles I have ever read, summarizing font usage, font management and how to solve font issues is this article by Kurt Lang. I feel it is a must-read for everyone:
Kurt has been a frequent poster on Apple’s forums and is constantly updating his article. If you benefit from his article, please consider making a small contribution via PayPal.