Tirelessly working behind the scenes to determine the best line breaks and optimal word spacing of your paragraphs, the Adobe Paragraph Composer is an option you’ll probably never need to change. Rather than compose your paragraphs on a line-by-line basis, the Paragraph Composer, in partnership with your Hyphenation and Justification settings, evaluates the whole paragraph to achieve the best possible typographic color; that is, the most consistent gray.
The only downside is that it can be confusing if you’re trying to manually break the lines of a paragraph, because the lines before—as well as after—adjust their position. When you edit your type, the Paragraph Composer considers the whole paragraph “in progress” and looks before and after the insertion point of your cursor to figure out how best to adjust the spacing. You can switch to the Adobe Single-line composer, which evaluates a paragraph line by line, but once you know why the Paragraph Composer behaves the way it does, it’s not disturbing to see your text shift as you edit—the results are worth it.