I can't see a reason to do this intentionally within a single account, but use cases with multiple accounts should be aware that what AZ has ID us-east-1a in Account 1 is not necessarily the same AZ that has the ID us-east-1a in Account 2.
But in the context of data transfer costs, this would actually increase the costs, because there's a small surcharge for Intelligent Tiering - and the only relevant storage class for sidestepping data transfer costs is standard storage (because it's the only one with free download), so Intelligent Tiering won't provide value.
1. Ask for discounts if you are a big AWS customer (e.g., spend $1mln+/year). At some point, they were huge for inter-AZ transfers.
2. Put things in one AZ. Running DB in "b" zone and your only server in "a" is even worse than just standardizing on one zone.
3. When using multiple AZ do load aware AZ balancing.