I have given two reasons of use Semantic HTML.
1.Always avoid the use of markup that present you HTML document.Like: element, attribute etc.
2.Try to use available markup to differentiate the meanings of phrases and structure in the document.
<cite class=\"booktitle\">The Grapes of Wrath</cite>
Above,the <cite> element is used because it most closely matches the meaning of this phrase in the text.