Margins and white space exist to help define the main reading area and the surrounding environment. They also provide visual relief when looking at a Web page. It is sometimes difficult to read Web pages not only because of the low resolution but also because the line length is often too long. A long line of text may make readers strain their eyes or lose their place when going to the next line. To account for this problem a Web designer can use invisible tables (border = “0”) to limit the line length to about 50 to 70 characters.
In terms of line spacing, to account for the longer lines of text and poor resolution, it is a good idea to add extra leading in between lines. For text that is 12-point font, implement leading of 14 or 16 points. For paragraph breaks, more common than indenting is leaving an empty line of space between paragraphs. This helps scanning a block of text and adds a visual rest to the reading. If a designer is using CSS, he can set the blank space using the “text indent” property of paragraphs.
Image source: Lynch and Horton. Web Style Guide: Typography. 5 Mar 2004. 16 Feb 2007.