Tons of shapes already there for you, you can group items, drag them around, change arrows quickly when making connections, overall great software. I also love the fact that you can save your data to dropbox and other platforms very easily and it uses common shortcut keys so you can save, copy, cut, paste, etc. quickly. Also, the export options are excellent, PDF, JPEG, SVG, XML, HTML are all extremely useful, we will take the PDF and send it to the client, or use the HTML/SVG version to post a graphic on the website, it is vector so it's scalable and lossless which means you don't need to measure and resize a bunch of times.
When your editing your diagrams sometimes the system can get a little glitchy, the drag points will be off or you can’t quite make a perfect square if you accidentally move a corner, it would be nice if it was similar to illustrator where you can’t modify an object shape unless you use a specific tool
If you need a simple and easy to use diagramming software this is the one, there is no risk because it is free, they have tons of symbols, and the interface is very intuitive, kind of like a illustrator feel