Hand-drawn diagrams feel casual and temporary. Sometimes these are good feeling to convey if the diagram is quick, might be incomplete, or get out of date quickly.
Excalidraw | Hand-drawn look & feel—you can use Excalidraw to create diagrams that have hand-drawn look
Why xkcd-style graphs are important - Chris Stucchio—using xkcd-like graphs for the very same reason
People don’t read
No one reads disclaimers, caveats, or explanations of graphs. They look at pictures. So it’s important to make sure that the pictures reflect your intent.