Why use separate php pages instead of one index
<p>For small projects I have been using one index.php page until now, with different ID's to display different actual page contents.</p>

<p>Would it be better to use separate pages instead of the index approach. E.g.</p>

<p>home.php<br/>
adduser.php<br/>
viewusers.php</p>

<p>instead of
index.php?index=home<br/>
index.php?index=adduser<br/>
index.php?index=viewusers</p>

<p>Thank you</p>

<p>Edit: I do the actual content generation through classes and separate php files, to keep the code clean and the index.php file uncluttered. I was just wondering what the benefit of using separate php files would be.</p>
