Why is it important to know how to sketch graphs when you have technology that can do it?

You need to know how the technology is doing it. Analysing data properly means that you need to understand what it is that you are analysing. Depending on any technology to do everything for you isn't a good idea because sometimes technology fails. What happens if the power goes out, for example? Or if your hard drive crashes the night before your report is due? If you know how to do the work, you can at least turn in something!