I am going to come down on
@Bill 's side here
I have taught both sewing machines and overlockers for a number of years and I have found the instruction books can be overwhelming for new customers.
I think if you go through the basics of threading etc and all the things you may use every time you sew first and then add the other bits in as you have the time and the need, people can often learn more easily and also remember it better.
Years ago some of the machines came with 2 instruction books, one for the basics you really need to know and one for more advanced techniques, personally I think it was a better system.