One important difference between detaching and joining threads, (besides the return value which I've rarely found a need for), is that once you detach a thread, there is no architected way for the rest of your code to find out if that detched thread has terminated or not.

It means that if you detach threads, you will have to provide your own mechanism for detecting if they are still running, or risk terminating your program before they've stopped and receiving the "NN threads still running" warning.