This may be a stupid question, but in finding my way around TOG DE for Year 2 (I use Firefox as a browser), I wondered about the difference between "opening" and "saving" the pdf files. For instance, when I click on, say, Week 12, a dialog box comes up and asks whether I want to open the file or save it. I have usually just been opening it and using it. Is there a benefit to "saving" it? What would the difference be between the two and which one is the "better" option?