Difference between usage of Dispatcher IO and Default

Question

In this question: Kotlin Coroutines choosing Dispatcher we can understand to use Dispatcher.Default on CPU process, like an image/video conversion and Dispatc

Answer 1

So basically they run on the same thread anyway. There is a real difference or in the end it won't matter each one to use?

Your quote from the documentation just details an optimization Kotlin introduced: when switching contexts between Default and IO, you don't pay for the expensive handoff to another thread; instead the thread itself moves to the other pool.

This doesn't affect the overall properties of the thread pools behind the Default and IO dispatchers:

• Default has a fixed size hardcoded to the number of available processors, because that's what makes sense for CPU-intensive tasks.
• IO is an elastic thread pool with a configurable max size. Threads in this pool are expected to spend most of their time in a non-runnable state, awaiting the completion of an IO operation, so it makes sense to have more of them than there are CPU cores.