you said..."When you say you send the image to a lab for a photographic output I assume you mean that you transfer a digital file for them to process in PS to meet the clients needs and not for them to print out."
I give my clients a inkjet as a soft proof, which they mark-up with a sharpie to let me know the changes and issues they have. After I get it back, I send the file to the lab for the clients enlargements. The clients get the PRINTS they ordered, but for magazines and publications, I FTP color corrected and sized <<dpi, gamma, color model>>CMYK files or greyscale files directly to the publisher or art director. As you can see there are a lot of color issues to deal with. I do give the final corrected file to the client, and they are free to do what they want with them, but for preparing files for magazines and such, I do that, and charge them for it.