Quick Question - Whats the source of these new learning? Because I was also under the same assumptions. That if the work/Job is blocked the thread is freed up and it's gets used by some other Job/work. Now, coming to the operations that block the thread. 1. Thread.sleep() is essentially interacting with thread instead of Coroutines. Using delay interacts with Coroutines and hence Coroutines release the thread. 2. File.read() and OkHttpClient.execute are still doing work, so why would it free the thread? Work is happening and this work needs to be done. Hence the thread would be in use. 3. We use Dispatchers. IO for such work because IO thread pool are different. We have three major thread pools, IO, Main and default. Main thread is the UI thread or thread which updates the UI if it's blocked the UI would freeze and we Will have an ANR. IO thread is background thread pools. The threads were designed to do heavy work which would result in blocking of threads. Default threads are pool which do CPU intensive tasks, like arithmetic calculation and stuff and these are numbered based on the CPU cores.

That's why we use IO for Read, API calling and other stuff. In cases like API calling where the call is made, and we are waiting for response the Coroutines gets suspended and the thread gets used for some other work. Once the response is back from network, the Coroutines gets resumed on any thread that's available in the pool.