[Geoff Bacon]

Using a csv file means that you have a single physical file (book) with multiple entries pointing at the individual songs within it.
You can use these entries within set lists and collections.

My advice is:

1. Use a csv when you know that "book" will not change e.g. it is published material.
   
2. Split the book into separate songs when you know it is subject to change (especially if by someone else)  - this preserves any annotations you have made when the book needs updating.
   

When creating a .csv file, it is a good idea to put all the files into a single collection (and also to include an entry that covers the whole book. This makes it easier to remove all the files should the book need re-importing using an amended .csv file

The .csv format has to be just right so look for examples on the site and experiment with just a couple of entries to see how it all  works.

Finally, you can't apply a .csv file to a previously imported book - it has to be available when the book is imported.

Cheers
Geoff