On a computer configured correctly, the errors are logged and the user or administrator may be notified when they happen. In my experience the most valuable be

On a computer configured correctly, the errors are logged and the user or administrator may be notified when they happen. In my experience the most valuable benefit of ECC is the detection of aged memory modules. All modern DRAM has a limited lifetime. Hopefully that lifetime is more than 5 years, but there are always some modules that may reach end-of-life much faster, especially on computers that are always on. While on a new memory module it would be abnormal for memory errors to happen more frequently than a few times per year, on an aged module errors may happen many times per day, or even many times per hour. I have encountered a few such cases that happened after several years of continuous using. Due to ECC I was notified about the errors and I could replace the offending modules before them becoming so bad as to guarantee data corruption. Another reason is that even if ECC cannot prevent a RowHammer attack, it makes pretty certain that a RowHammer attack will be detected immediately (because the attacker cannot control the location of the flipped bits, and even if there are many errors, so they will be miscorrected, in most cases they will still be detected and logged and the administrator should always be instantly notified when there are two or more errors per day, as this will never happen normally).