I never use the monochrome mode (or any other modes) on my camera. I want to capture everything the sensor and processor will allow me to and then choose at home how to deploy all that data. To that end, I shoot in RAW mode in the camera, do a "neutral" processing of it in Adobe Camera Raw, then send the result into Photoshop as a Smart Object which I process into monochrome in Nik Silver Efex Pro 2. This workflow first of all produces very, very good results. Prior to discovering it, I had never found any software that could equal the control and results I achieved in the wet darkroom. Second, this process is non-destructive right up until the moment I choose to save the final result as a JPEG to share with other people. What this means is that I can go back and change the processing of any one step at any time without having to restart from scratch. Feel like I might want to go back and make it look like I'd used a yellow filter rather than an orange one? Tweak it. Want to go back and add some extra contrast to the shadows? Tweak it. What to go back and bring the tones of the model's dress down to a darker value without bringing her skintone down? Tweak it. Want to add contrast and sparkle to her eyes without also emphasizing skin defects? Tweak it.
It's a very, very powerful workflow that I gain more appreciation for each time I process a shoot through it.
If you shot in your camera's monochrome mode, you'd be locked out of all of it.