title: Is there any particular reason to store user's timezone when I have already stored user's local time and UTC time - PHP/MYSQL?
body: <p>I was wondering why should i need to store user's timezone as many suggested when I have two columns already in my db table <code>local_datetime</code> and <code>utc_datetime</code> which are used  to show how long ago a comment was posted. I can use the <code>utc_datetime</code> and convert it to user's local time and the <code>local_datetime</code> helps me sorting results by a particular day for a user. So my question is, what is the purpose of storing timezone??</p>