Any use case where you cannot afford data corruption requires ECC memory. A single bit flip in a JPEG image can totally ruin it (and you might not notice at first, because the thumbnail doesn't change, allowing the corruption to spread to backups...)
Particularly susceptible to memory errors are applications that keep data cached in RAM over longer periods of time, such as file / database servers.
One use case for ECC is ZFS.
ECC is probably less important for ZFS than it is for just about any other filesystem.
That’s simply not true. ECC is key to avoid bit rot.
ZFS includes strong checksums over stored data. Bit rot is more protected against with ZFS on a non-ecc system than most other filesystems on a system with a theoretical/impossible 0% memory error rate.
And ZFS+ECC is better than ZFS without ECC.
Exactly my point. Then why the need to down vote my comment? The statement that ECC is irrelevant for zfs is blatantly incorrect. There can be bit rot in ZFS checksum values without ECC. Ask Allan Jude if need be.
It's not irrelevant, but you should still use ZFS if you care about your data, even if you don't have ECC.