If you are parsing a big thing of text, there is no opportunity for your thread to pause the CPU and say "ok other threads, I have to wait on some external data

If you are parsing a big thing of text, there is no opportunity for your thread to pause the CPU and say "ok other threads, I have to wait on some external data" and then hand over the CPU resources. But if you are trying to make a network request, disk or memory access, or any HID stuff, you might have to wait on that thing to do it's job and get back to you. At this point you can tell your thread to raise it's hand and say "hey, I don't know how long, but I know I need to wait for this thing to finish, so while I wait someone else can use the CPU, but when I am done waiting, I will need the CPU back." This is the core idea of "cooperative threads" or green threads or co-routines or any sort of thread that is at the language runtime level and not at the OS level. https://en.wikipedia.org/wiki/Cooperative_multitasking https://en.wikipedia.org/wiki/Cooperative_multitasking So consider if the task you are doing is asking for data from "somewhere external to my thread" then you might be able to make that call non-blocking to enable more throughput. Hope that helps explain it!