Some simple responsive structures keep text in a single column that expands and contracts with the size of the device. This can be an elegant, appropriate solution — except when the font size (instead of the column’s width) is used to preserve the ideal measure.
We’ve learned not to set text too small, but text that’s too big also poses a problem. When type gets too big, the reader’s eyes try to follow their usual pattern. But a font size that’s too large takes up more horizontal space, and it interferes with the horizontal flow that readers have established using their foveal vision and their pattern of skipping words.