The ease of use, the way it can be used to create different types of diagrams and charts, the flexibility to customize everything about your chart/diagram (colors, fonts). Sometimes I feel like there are some features that could have been added but aren't available yet or haven't received enough attention from developers. For example, you cannot save a diagram as an image so if you want to share it online you will need to convert it back into text. There is also no option for exporting data tables directly to Excel. It's great because I don't have to spend hours creating graphs and charts by hand every time I need one.