Emphasis patterns are used to highlight key information, and focus readers’ attention towards it.
Attention is like a spotlight, and when readers pay attention to something, they always do so at the price of ignoring something else. You can ensure that key information (e.g. deadlines, exceptions, counter-intuitive information) is not overlooked by giving it a level of visual prominence matched with its actual importance.
Emphasis patterns should be used sparingly and only when it really matters, so that the reader can identify quickly and without uncertainty what you want them to pay attention to. Emphasizing too many pieces of information is confusing and counterproductive, so choose wisely and coherently what bits needs an extra kick.