When you type a headline, the browser spaces it using the font's built-in kerning table: a list of letter pairs, each with a fixed adjustment, chosen by the type designer for reading sizes. It's usually right. But it can't see the whole word, doesn't know how big the type is, and can't tell when a gap spells a different word. These are the moments a graphic designer overrides it.
Each example shows the browser's own layout next to a hand-respaced version. Blue figures are the designer's adjustments in 1/1000 em, the unit InDesign and Illustrator use for kerning.