As in traditional print publishing, high-quality Web sites adhere to established type style settings consistently throughout the site. Consistency gives polish to a site and encourages visitors to stay by creating an expectation about the structure of a text. If sloppy, inconsistent formatting confounds this expectation, you will confuse your readers and they may not return.
You should decide on such settings as fonts, inter-paragraph spacing, the size of subheads, and so on and then create a written style guide to help you maintain these settings as you develop the site. This step is especially critical for large sites that incorporate numerous pages.
If you choose to use CSS you will have powerful tools to maintain the consistency of styles throughout your site. This is particularly true if you opt to use a master style sheet for your whole site via the "Link" option in CSS (see Cascading Style Sheets).