It depends on what you are optimizing for. There's a tradeoff between wall time (start vs end time) and work time (time spent on a specific task, not counting

It depends on what you are optimizing for. There's a tradeoff between wall time (start vs end time) and work time (time spent on a specific task, not counting other work). Some level of multitasking increases throughput substantially with a minimal increase in wall time. This is ideal. Too much or too little creates waste.