Do you (and why if you do) shoot in B+W on camera?
RAW FTW
If you set your camera to B/W then the jpeg preview / image will be B/W but then you can tweak the conversion in PP (channel mixing).
Most cameras will allow allow you to convert to B/W, sepia or cyanotype in camera giving you a preview if you're shooting in colour. JPEG shooters should shoot in colour and then convert as you can't get the colour information back.
Yes, sure you can't get the colour back, but as I said, I prefer the B&W output of the in-camera preset to what I get from ACR.
I could shoot in RAW+Jpeg but then if I liked the b&w jpeg output from the camera, the RAW would only be a large file that I wouldn't use.
I personally am not one for lots of photoshop/lightroom processing, I don't have time. (Though if I had time I might work on getting a few LR presets that would give me what I want, saving time later).
If you have time to spend on importing and processing lots of RAW files that's fine, but I like simplicity in my shooting and editing because I'm more likely to get a simple edit right.