Hopefully it will make more sense once you get the plugin installed and click the Modify ePub button to see the options. Don't forget there is a Help file for that plugin as well, which describes in detail what each of the options do. Perhaps then the two options we suggest you use will make a bit more sense.
Don't worry about the rest of what I said - I just wanted to "complete the post" in terms of information. I personally hate it when people make generalisations saying that doing such and such is a bad idea without backing it up to say why. Besides which, quite often others can point out that actually the thought is wrong because there is another way around it - in this case I don't think I'm wrong but calibre continually improves and changes so quickly that the information may not be relevant x months from now.
