Use case for previous row Id are simulations of iterative formulas: Mortgage financement, savings estimations, Intermediate sums checkups.
Another useful idea for that would be to have a Fold operator, that can iterate a formula a number of times:
Fold(list, formula, VarLisr, VarCumul, StartCumul)
e.g. to compute savings of a 1% yearly plus 100 added every year, over 20 years
Sequence(1,20).Fold(s*1.01+100, i, s,0)
But again, we would need to pass a formula for argument, not a value, like Call should do.