Too Many Fonts...

An example of why too many fonts can be confusing - a re-imagined* Spotify on iOS.

 

Don't think this is so bad? Check out this quote and article from Nigel French at Adobe Create Magazine:

"A good principle to live by, whether you’re new to typography or a seasoned pro, is to keep it simple. Or to put it another way, don’t use too many fonts. Just as mixing too many colors on your palette will likely result in mud, mixing too many fonts on a page will probably result in a confused message."

* - for demonstration purposes only - not the original app's choice of fonts!