I can see that nodes of a line are in different places when comparing square caps (indented from the ends) and butt caps (on the ends), but in what situation would I need one over the other?

I often switch round to square ends and have used mitre joints when joining different colours or transparencies; but I have yet to find a need to switch square for butt or vice versa. They appear to be one and the same, although I'm sure they're not. Would anyone care to give a scenario? Treat me as a child learning my ABCs.