Split lock washers do nothing?

In my experience there are two kinds of split washers. Ones that load the fastener and ones that load and dig into the material. There are situations where you don't want material being dug into. Most failures come from old, typically flattened with age or corroded washers and worn out threads on the bolt/threaded holes from multiple uses.
Improper torque both ways and contaminates on the threads can cause loosening too.

Like most thing, they work right when used right.