Mandatory for justified text; optional otherwise

Hyphen­ation is the auto­mated process of break­ing words between lines to cre­ate more con­sis­tency across a text block.

In justified text, hyphen­ation is manda­tory.

In left-aligned text, hyphen­ation evens the irreg­u­lar right edge of the text, called the rag. Hyphen­ation is optional for left-aligned text because the rag will still be some­what irreg­u­lar, even with hyphen­ation. Hyphen­ation doesn’t improve text leg­i­bil­ity. Con­sider turn­ing it off.

As line length gets shorter, hyphen­ation becomes essen­tial. Why? With hyphen­ation off, your word proces­sor can only break lines at word spaces. As the lines get shorter, there are fewer words and hence fewer pos­si­ble break points in each line, mak­ing awk­ward breaks more likely.