Like all similar translation tools, it is incredibly inaccurate. Mostly, it can give you a rough idea of what the text is about, but sometimes even that is too difficult.
In the long run, you may start to rely on it too much. You shouldn't rely on it at all, as there are many things it just doesn't know. It might give you entirely the wrong idea about the meaning of a particular sentence, for example.
These tools are OK if you have found a website in a language you don't know and you need to find out something simple. But for proper translations, they are no good at all.