Why do we need Italic/Bold Font Files? What is the difference between HTML Italic/Strong tag and a Font? [closed]

Question

Why do we need italic/bold font files if we have <em> <strong> that can italicize and bold respectively ?

Arial Narrow Italic Arial Narrow Italic Bold

Is there a special scenario where having the file can actually make it more perfect than what browser can render ? For example browser might have a generic way of making italic vs bold however a specific italic/bold file could make it much better ?

How do I actually use them in the application ? For example I need Caslon 540 Caslon 540 italic , and I get two files for both . Do I treat them as entirely different font like

@font-face {
  font-family: Caslon;
  src: url(fonts/Caslon.ttf);
}

@font-face {
  font-family: CaslonItalic;
  src: url(fonts/CaslonItalic.ttf);
}

This looks simpler to implement ?

or do I actually have one Font with differnet font:style specification ?

@font-face {
  font-family: Caslon;
  src: url(fonts/Caslon.ttf);
    }

@font-face {
  font-family: Caslon;
  src: url(fonts/CaslonItalic.ttf);
  font-style: italics;
}

Does this have an overhead that you need to have a font-style:italics embedded into each element's html attribute or would automatically detect that its CaslonItalics ?

There is a somewhat similar question in its essence here : <strong> vs. font-weight:bold & <em> vs. font-style:italic

Answer 1

1. The end-user's browser may not have the font installed. Remember, the content is being rendered client-side, not server-side.
2. There may be something about your content that requires some aspect of the specific typeface (odd kerning, specific sizes available, special characters, etc.) for best readability.
3. The <i>, <em>, etc, HTML tags don't do anything to the typeface at all -- they tell the client how they should be rendered, and the client chooses the appropriate typeface.
4. You can use CSS to tell the rendering engine to use a particular typeface for italics, like i, em { font-family: Caslon; }'. This is discouraged, though, because you're taking choice away from the reader -- who may not like your typeface choice.