Digital BW, The Print

Every once in a while, I forget to change the mode to monochrome after
I convert to B&W in PS3.  After layers are added, it is impossible to
convert from RGB without flattening the file.  Question: does it make
a difference whether you work on a B&W file in RGB or monochrome?  99
times out of 100 I catch the problem before I print and send a
monochrome file to my 2400 in ABW mode.  

Thanks,

Steve