Many pages that use the <font> tag to define the font styles on the page are much larger to download than pages that use CSS.
The problem with the font tag is that it can be cut off by many other tags on the page. For example, in a table, every single table cell needs to have an additional font tag to make sure that the font remains the same throughout the table. If you use style sheets, you can define the font style for every table cell with only one style property.
