In typography and page layout, leading refers to the distance from baseline to baseline in successive lines of type.
Kerning refers to the spacing between two characters in a proportional font, while tracking uniformly spaces the letters of the entire word. These design concepts affect the overall vertical rhythm, or visual flow, of your composition while typesetting.
Why is it important?
Too little leading and kerning can fatigue or overwhelm the user with long lines of text (measures) and short distances between baselines. This makes it hard to keep your place from one line to the next. Too much leading and kerning can disrupt the visual rhythm and create “rivers”, or large amounts of uneven space, in your text blocks.
Properly set type balances the flow of content and will provide the user with an effortless viewing experience. Don’t make it hard on your users to digest your information. Those types of designs simply don’t convert. Instead, help the user’s eye across the page through proper leading, kerning, and tracking techniques.