Did you know that you regularly read type set in size 8, or even smaller? In printed materials, captions and less important information (think: photograph credits, newsletter headline subtext, magazine staff listings) are usually reduced to something between 7.5 to 9 points. We generally read that size type without much issue, like glasses. The reason why we can comfortably read those small sizes is because the designers chose an effective font that keeps its clarity and legibility when shrunk.
Designers don’t make the font that tiny to give you a headache. They do it to establish a font hierarchy. Our brains interpret the biggest size as the most important and the littlest size as the least important. So we can create a hierarchy of font sizes to structure our work and communicate even more clearly.
The font hierarchy is important, but so is picking a font which is clear at the sizes you want to use.