Use boldface text sparingly. Avoid the temptation to use boldface text to emphasize words within a passage of text. Bold text is like a magnet to our eyes, and if used incorrectly, ruins the continuity of your text. I once heard someone describe paragraphs containing boldface text as looking like chocolate chip cookies. And that' s an apt description.
Bold words stand out like little chocolate bits.
Bold text is best used in headings, captions, logos or sometimes at the start of a paragraph as a stylistic device. In place of bold, consider using italics for emphasis. Italics blend in more smoothly with surrounding text, yet clearly indicate emphatic stress. Reserve boldface for items that can be set entirely in bold, and avoid mixing with normal, or non-boldface, text. Bold face text within normal text provides too much emphasis.