Why declare PHP variable type in a comment?

I'm fairly new to PHP, and I just started using NetBeans to develop my PHP code.

Out of the blue, as I entered a variable in a query, a dialog popped up and asked me to complete a comment to hold the variable type. I did some investigation and found that this seems to be a popular feature of NetBeans, but I couldn't find any information to explain to me why this was the case.

Why would someone want to place a PHP variable's type in a comment? Is it for development use, or does it actually benefit the code itself? Is it integral, or optional?