It’s a super easy way to start new coroutines. Calling a suspending function like delay from a plain old function would normally give you an angry red compilation error. But wrap it with runBlocking, and suddenly you’re free not only to call all the suspending functions you like, but also to use coroutine builders like launch and async.
Using runBlocking in the main function like this is no problem. But when was the last time you actually added code to the main entry point of a real production system? When you’re working with coroutines, you’re more likely to be deep within your app’s code, and that’s where things get more complicated.