Can someone ELI5 where this is going to be valuable?

If you set up Postgres read replicas, make sure your queries are covered by appropriate indexes, and your hot queries are handled by Postgres from RAM anyway - do you really need a separate Redis cache?

I feel like anytime I'm going to pull in Redis for a cache, it's going to be for data that I'm not interested in having guaranteed persistency for, like session tokens, and so it'll be for data that I wouldn't be storing in Postgres anyway?