How much is Kibana ILM cost-effective?

Question

I understood that the hot-warm(-cold-frozen-deleted) lifecycle is a great tool, but I haven't found much numerical documentation: one of the few documents that gives examples with numbers (and not just feature descriptions) is this blogpost. In the hot-warm example without roll-up, it seems to me that the main storage optimization is given by the number of replicas:

• one day of data = 86.4 GB
• 7 hot days = one day of data * 7 days * 2 replicas = 1.2 TB
• 30-7 warm days = one day of data * 23 days * 1 replica = 1.98 TB

There are other resources like this webinar, yet it doesn't distinguish between storage usage and RAM usage. Is there an official document (or third parties experiment/report) that shows if and how much the cold/frozen/"non-searchable snapshot after deletion" phases optimize the storage usage? Or is only about less RAM usage?