A flowchart with a hyperlink to more detail.
Here's an example of how powerful Visio diagrams can be: If a portion of your diagram needs additional detail, you can create that detailed portion separately and add a hyperlink to it.
In this example, there's a hyperlink on the Trials shape. By clicking it, people can discover more details concerning that particular step in the process.
Now's a good time to mention that other Microsoft Office programs like Microsoft PowerPoint® and Microsoft Word also help you make diagrams. However, those programs don't give you as much room to create a diagram as Visio does. They also don't have as many sophisticated options for diagrams.
When you need a large and detailed diagram, Visio is the right program to use. But if all you need is to make a modest diagram in a hurry, use your favorite other Office program.