Not sure where I would ever use it, but I would love to be able to produce these xkcd-style plots in IDL, currently available in Javascript with d3, R, and Python with matplotlib.

xkcd-style plot

An academic paper has been written about this and even provides a Processing implementation. From the abstract:

Results suggest that where a visualization is clearly sketchy, engagement may be increased and that attitudes to participating in visualization annotation are more positive.

So it appears that a plot that looks like a sketch indicates to viewers that it is not a “final” product.