redis and PostgreSQL, functionality cross-over?

[TimH]

I've had to disable BerkeleyDB on a new install as there seems to be
something wrong with it (FreeBSD 12.1).

I figured I would set redis up instead, as it appears to be the way to go.

I am already using a PostgreSQL database, which allows some user/domain
level white/black listing and (I Think?) Penpals functionality.

What functionality is enabled by using a redis database that I don't
already have in my psql db?
  Nanny?  (not sure if I am using that if bdb is disabled;
           not sure I was using it before) snmp?
  Ip address reputation?  How does that work (where does it get its info?)?

Is there a better way for me to find this info other than the release
notes?  I always feel like I am missing context there.

--TimH