We use Citus. Very similar performance properties to DIY sharding but much more polished. Currently at 7 TB, self hosted. Growing roughly at 100 % per year, write-heavy. Works fine for us.
Pitching Citus ran into issues where people were hoping it would handle sharding transparently, which isn't the case. But for someone who's evaluating rolling their own sharding, being able to manage sharding keys explicitly is how Citus allows efficient joins based on your workload. So yes, if you're looking to roll an unmanaged sharded postgresql cluster, consider starting with Citus
First, the data size is growing and we didn't really know the growth rate in advance. Sharding gives you some flexibility in the infrastructure sizing. And yes, you don't want to wait until the last minute.
Second, it helps us to spread the disk I/O. Possible on a single machine if you're a little bit careful with disk types and sizes. But again, the overall load still grows.
Third, all the bulk operations take a long time on a single server. Each of the distributed servers takes about an hour to back up and 2-3 hours to restore. I'd feel uneasy if it was much longer.