It’s very easy to desaturate your picture to have a black and white photo. You can also use the options provided by many applications to quickly change from colour mode to black and white mode.
But if your subject wasn’t properly exposed, and the lighting wasn’t right, you’ll end up spending a good deal of time post-editing. Using a black or white backdrop always helps with portraits if you just want to showcase the face of the person.
Use bonce method to create the natural effect of half-lit face, avoid doing that in post edit, it never looks natural.
The reason I love black and white portraits is that I can show emotions, and more importantly, tell a story.