There are good reasons for many of the rules in typography.
To indent or to space?— that is the question. Whether 'tis better to set paragraphs using space or indents is your choice. But alas, choose one method or the other, not both. Look at the photos to the left. You will see that the blue photo on the left shows an example of paragraphs separated by indentation, not space, while the gray one on the right shows the use of space instead of indentation. Most importantly, notice that the first paragraph in both photos is not indented. Why? Because we use indentation or space to give the reader a clue that a new paragraph is starting. If it's the first paragraph, the reader already knows it's new—no need to give a clue. So...when typesetting paragraphs, pick your poison. Either space or indent, but don't do both!