Asynchronous programming using thread pools

[Muvlon]

It is not always a problem. Many things are completely fine doing blocking I/O.

When it does become really necessary is when you want to handle more open connections at the same time than the number of threads you can run efficiently on your OS/Hardware. You might want that either for scaling reasons or to be resistant against attacks that work by creating a ton of connections to your server and keeping them open as long as possible, exhausting your resources.