If you subscribe to your threads or responses to get the updates for what you have contributed, you should click in the box under the thread or response for the same. By doing so, you will be getting system alerts and emails every time someone gives a response to the thread in which you have responded. So, this option should be wisely used. You should use this option only when you really need a message in your alert and email. I will explain it to you in a simple manner. Suppose you give a response in a thread and subscribe for the same and there are 60 responses to that thread, then you will get 60 alerts in your alert box and 60 emails in your mail box.
"Teaching is my passion & sharing of knowledge is my motto"
Lead Editor & Platinum Member at ISC