When using revenue split in the subscription billing module, there are different allocation methods available. The "zero amount" allocation method is applied the following:

"Zero amount – The parent item retains its unit price and net amount. All child items have a net amount of 0 (zero)."

But at the same time, there is a limitation on how deferral schedules can be applied to revenue split items:

"The parent amount can't be deferred."

For this specific allocation method, it would make sense to defer the parent item and not the child items as only the parent is having an amount stated. In general, the deferral schedule creation must be totally applicable to this. Otherwise, the allocation method "zero amount" is useless.