In making ePub formatting decisions, the nature of the print book should be taken into account.
The standard and most flexible ePub format is 'Reflowable," because it presents a page display that is adaptable to the device on which the book is being viewed.
To make the "Fixed or Reflowable" decision, two factors should be considered: page integrity and typesetting "significance."
Page integrity: If print layout and pagination needs to be preserved, fixed layout must be chosen.
Typesetting significance: If typesetting carries a message in the book, then fixed layout should be considered.
(Concrete poetry, for instance, uses typesetting and layout to reflect meaning.)
In such a case, it's best to opt for a fixed layout file to preserve the original form.
On the other hand, formatting anomalies like indented verse lines can be reflected in the reflowable format.
If there is doubt about format choice, you could consider producing both formats.