Does it benefit to keep the file in 16 bit mode after grayscale/desaturation?

As much as it does in color, perhaps even more.

The main value of working with 16 bits is that further edition of the image that will end up merging different RGB values into one, or creating gaps between used RGB values will have visible impact on the image.

This problem is IMHO as severe in B&W than it is in color.

Regards,
Bernard

If you are using a B&W printing technique that uses curves to control the tone (such as the MIS UT2 ink set) the I have read that keeping the file in 16 bit avoids some problems of posterisation

keith

16-bit editing helps avoid posterization, and is just as important or even more so in B&W, since even in the best-case scenario there are only 16 bits per pixel vs 24 for 8-bit RGB color. I recommend doing everything you possibly can in 16-bit mode. If you are editing in straight B&W (no toning or tints) there is no disadvantage in converting to the grayscale gamma 1.8 edit space (if using ProPhoto) or grayscale gamma 2.2 (if converting from sRGB or Adobe RGB). This will reduce the image file to 1/3 of its size in RGB mode, which you're not using anyhow.