This article explains why using styles to format documents is so much better than using direct formatting.
Direct formatting refers to selecting text and choosing a format for it. When more than one format is required, each must be chosen individually for the selected text.
Direct formatting has its place, but using it exclusively ignores one of word processing's very best features: Styles.
Problems using direct formatting:
Styles overcome all these shortcomings and also save time and effort spent formatting.
To learn how to format using styles, see Formatting with Styles.