[l_t]

Making plain-text diagrams isn't as hard as you might think, especially using "overwrite mode" (that weird thing that happens when you fat-finger the insert key!)

But many of these tools work by allowing you to express the _intent_ of the diagram without having to draw it out. They're basically markup languages that get "compiled" into diagrams. PlantUML is a good example: http://www.plantuml.com/plantuml/uml/SyfFKj2rKt3CoKnELR1Io4Z.... With these tools, you can make diagrams much, much faster (but usually with less nuanced control over presentation)