On many websites, when you log in, it gives you the option to "Remember Me". Next to that, on some websites, it shows what "Remember Me" means. Why would it have to explain what "Remember Me" is? After years of websites that have "Remember Me" buttons, doesn't everyone know what it means? Isn't it just useless code to explain to the user what it means and why you might not want to enable it?
I think your question is somehow based on a stereotypical view that internet has been here for ages and everyone knows how to use it, thus labels such as this particular one seem to be redundant. I actually believe that explaining every action accessible by the GUI is a very good idea, especially in cases where you can't exactly predict your target (age group, gender, etc), but still would like to encourage every user to engage into a precised action (let's say, buying something online). Also, this sometimes might have something to the security aspects - imagine an unexplained "remember me" button at your online payment system*.
*Actually, surely there's none at all, I just wanted to give a comprehensible example.