Tasks in the kernel are frequently postponed until the yield or effect is actually needed. The motto was, work postponed is often work avoided. We would avoid preparing a key until it was absolutely needed. Ditto unpreparing a key, or nodes. A few times added temporary code to measure how often it was avoided. We were amazed how often this was. We never found a case where we would win by removing the postponement. Indeed we thought of more later which were not implemented.