One application is the "past habitual."
She would sing in the shower.
See, e.g.,
The Evolution of Grammar: Tense, Aspect, and Modality in the Languages of ... By Joan Bybee, Revere Perkins, William Pagliuca
or:
English Grammar: A function-based introduction, Volume 1 By T. Givón
Another application is dreaming/imagining in a past time:
Dusting Off the Ashes: One Man's Personal Journey Through ... Maria Heaton M.S., Maria Heaton - 2010
In my dream, I would keep saying to them, “We need to leave the building. It is not good. It's not good.”