I see a pattern here that society is starting to assume that a webpage can only be browsed with a web browser. A judge even decided that accessing data you should not see in a webpage is illegal, so I guess you aren't supposed to do anything with HTML other than view it in a browser...
So basically a computer is just a blank device with no real use unless you install an Operating System on it, like Windows or Linux. That controls how your computer actually behaves: how you install programs, what you see on the screen, how your hardware is managed... Most computers come preinstalled with Windows, but you can install Linux (or other systems), and many people find it works better for them. You can also install both, and also there are many variants of Linux to choose from, so there's more to it. Hope this helps.
It could also modify memory. If the function writes to a global variable or to an address passed as a parameter, then it makes a difference. For example, would you say the void function 'free()' is useless?
I'll just drop my two cents here and say that we as humans should not rely for our way of life on anything being impossible, because most likely, it isn't - it's just that we haven't actually done it yet.
I see a pattern here that society is starting to assume that a webpage can only be browsed with a web browser. A judge even decided that accessing data you should not see in a webpage is illegal, so I guess you aren't supposed to do anything with HTML other than view it in a browser...