In most browsers, this would be italics but it could also be rendered as something else. In any event, the text will be emphasized in some manner. The same is true for bolding text. The boldface tag is also a Netscape extension tag and so not recognized by a number of browsers. In most browsers this will be boldface, but it could also be something else.
Content based markup allows for browser independence.
Knowing the meaning of a piece of text through a content based tag allows a browser to pick the best way possible to display the text on the platform it is running. You are encouraged to use logical tags because the browser can then pick the best way to display the text on the screen. If all this sounds too confusing, don't quit on me. Just follow through on the following examples involving logical tags. It should all become clear.