Benefits of using the new Asio4All inputs/outputs – Bitwig Forum

The only thing that is changed is that ASIO channels are now automatically detected and named after the name of your Audio interface.

So instead of something like “output 01” you now see the name of your interface, with all detected outputs shown under that.
You probably have set asio4all as your audiointerface, so that’s why you see it listed in the track output menu.

How you use it has not changd. It’s used to set the output from a Bitwig track to a phyiscal output on your audio interface. for example if you have an audiointerface with lots of channels and want to send those to a mixingconsole. or to hardware fx.