[onion2k]

This is a good illustration of exactly why this font is useful - you want to focus on typography, so you think you need to see text. Given a mockup that needs comments about the layout, or color, or whatever you'll be looking at the wrong bit. This font lets you can see where the text goes, but you can't spend time worrying about the font, weight, kerning, etc so you'll only be able to give feedback on the bits that need feedback.

Obviously if a design needs comments about the typography the designer wouldn't use this font.