Jims correct on both counts CMYK does increase file size, mainly due to the fact that you have an extra channel in CMYK mode.It is an important point that he raises,especially for Poser post production people as if you have saved the Poser file as a Tiff you already have an extra channel where the mask has saved as an Alpha channel.This means your starting to get into some very large file sizes and if you were to:- for example,be entering the Zygote Calender contest where the final image is going to be a CMYK 11" x 8.5" image at 300dpi it starts to become almost unworkable on a smaller machine. Another disadvantage is that a number of the photoshop filters only work in RGB mode. I sometimes do work on video covers that are to be printed and to be honest all I do is work in RGB mode with the CMYK preview switched on,to give me a better idea of the final image and keep in mind the fact that it will look a little duller without the screen light behind it.When I,m finished I convert it to CMYK and hope for the best.So far I,ve got away with it.(touch wood)