Apple’s Icons Have That Shape for a Very Good Reason – Medium
On the right you see what curvature continuity looks like. The curvature comb transition is a curve itself, starting from zero curvature. There’s no sudden break in curvature and, as a result, the highlight is smoother. This difference in curvature is harder to spot in an icon, but the important thing is that now the icons and the hardware are part of the same design language.