Inkbunny's main server has mirrored SSDs for database storage. However, if both were to fail, say, due to a power surge, we might have to restore from a nightly backup. No more. Streaming replication provides a continually-updated copy on our secondary server; at the same hosting facility, but in a different hall. It's not synchronous - that'd reduce main server performance - but it's typically within 200ms.
In the meantime, write-ahead log compression has reduced the bandwidth we require for it to ~5MBit/sec - just 1/20th of our main server's capacity, and 1.5TB of our secondary server's 100TB/month allowance.
We benefit from using unlogged tables for search results, which we keep around for a bit, but don't need to persist in the event of a crash - they're muchfaster, in part because their contents aren't replicated.
Of course, replication wouldn't save us from a bug in the site, attacks, or staff error, so we'll retain nightly/weekly off-site database backups. Images are also backed up nightly (if not cached sooner).
This also opens up the possibility of cascading replication, where the secondary server feeds live off-site backups - useful in the event of a catastrophe affecting the entire datacenter. A project for another day!
The change does not significantly decrease disk space on the secondary server. We have enough for over three years' usage at current levels, and we're likely to upgrade both servers by 2018.