Computers are fast. I once worked on a service sitting at the top of a deep RPC stack. Stack traces were often folded into RPC error messages to help diagnostics. Well, if you have a failure at one layer, propagated to the next layer, and the next layer, and sometimes replicated for each looked up item (to support partial failure semantics), then you can end up with gigabytes of stack traces in memory for some fraction of time. Very hard to figure out until tasks started dying and leaving behind heap dumps during a wide-spread incident at a lower layer of the stack.

I joined the team long after this was in production, but I can testify that the service has a lot of moving parts and attributing the reliability / efficiency costs for a specific issue was challenging.