With the proviso that you must be connected to the Internet and have it all set up correctly.
It uses the same Apple servers to do the dictation as Siri on iOS, which is why you have to do it in bursts to allow the recording to be uploaded, the software to analyse it and then to send back the dictated text.
Apple obviously has shares in the power companies and ISPs that are required to fuel all this foolishness and put another boot into an already damaged environment.
You could just install Dragon Dictate on your Mac which cuts out all the unnecessary toing and froing, along with its delays, but then that wouldn't be "Cooool!".