What you need timer interrupt for is “true” preemptive multitasking/threading. For many applications that makes quite large difference in programmer comfort (ie

What you need timer interrupt for is “true” preemptive multitasking/threading. For many applications that makes quite large difference in programmer comfort (ie. you can just run CPU-bound computation without any regard to yielding to other tasks). On the other hand you can successfully create create multitasking-like user experience without any OS level support for that simply by making everything event-driven.