Even a single rare rollback can kill a prod DB. We had a situation when a bug in our code caused a series of huge UPDATEs in Oracle DB and LOCKed some critical tables. After ~2 hours we found this session and killed it.

The problem - we had to wait for 2 more hours with dead prod while Oracle was rolling back everything. In Oralce killed sessions still hold their locks while rolling back.

In Postgres rollback is almost instant.