You could be laying back in your bed with your mac open on your desk, and ask it to start playing music without even having to get up, as I demonstrate in this video
I've based my instructions of this tutorial, however since my instructions use Automator instead of a keyboard shortcut, they will work on more people's setups! so go ahead and follow these instructions until instruction 10, and then instead of assigning the dictation command to a keyboard shortcut, we're going to create a workflow with Automator and run that instead.
All you need to do is open up Automator (a program that comes pre-installed with macOS that many people simply overlook) which can be found in spotlight search. Then create a new workflow
Now you simply add the action "Launch Application" which can be found by searching for it under the Utilities library, and as the Application parameter for this action we just select Siri.app
Now you save this workflow and assign the voice command to the workflow you saved. Easy!
One thing to note is that it sometimes works TOO well, in that siri will activate itself if you're listening to audio on the speakers that contains the words "hey siri"