with better planning, you'd be able to schedule these various tasks in advance in a way which let you do continuous blocks of work at a time while waiting for other things to complete, but without proper planning, reactivity forces you to jump btwn tasks haphazardly, wasting time
there are many other multitasking failure modes known to computer science, and mostly all of them show up in our personal lives as well; after all, CS is the study of processes, not computers, and executive function disorders manifest in a poor ability to manage our own processes