The question to use 8 or 16 color continuously comes up. I have tried to get a definitive answer to this question, but found nothing concrete. I have been using 16 bit for some time now. Mostly due to the advice of a friend who happens to be a professional photographer. I have to say I don't really notice a difference in my paintings, but I kept at it since it might help with better print results. This question wouldn't be coming up again if it weren't for the fact that I am looking to move to a Linux environment. Unfortunately I use Photoshop and Adobe only supports Windows and Mac OS's. But the alternatives,such as GIMP among others, only support 8 bit color. So do I really need 16 bit color?
Basically what I have realized, which may or may not be so obvious to all, is that when viewing images on our computers, we are looking at 8 bit color (8 bits per channel). Considering that we also watch movies, TV, view photos, paintings etc on these systems, we are used to looking at 8 bit color. The other side of this is that the same media files are usually created from higher bit colors and then reduced, leaving me to believe that I should stay with 16 bit over 8 bit color. The disadvantage of 16 bit color is the added file size and memory usage. Yes, file size isn't that big of a concern with the low cost of storage these days, but high memory usage will catch up to us all. I run a quad core system with 8gb of memory, with files that are 16 bit, 300dpi, with multiple layers, that can run into 500mb size or more (which isn't that uncommon), they can take 2-5 minutes to load and save ...I have timed it. I believe in efficiency and only using what you need to eliminate waste ...basically keep it simple. If you don't need it, don't use it.
So what is 16 bit color needed for? The short answer is that it should be used if one starts with a plate (photo or image to paint on) or touching up a photo that is already in 16 bit. One doesn't want to lose the color information that already exists. I'm a painter and since I don't normally use plates with 16 bit color (normally found with RAW image files) or I'm starting a painting from scratch, then there is no color information to be lost ...it doesn't exists.
My conclusion is that if it starts in 16 bit color, work in 16 bit color unless you know for sure that you will not need it. Otherwise work in 8 bit color. Photographers will normally use 16 bit color since they are more likely to be working with RAW images and painters will use 8 bit color allowing for efficient memory and resource usage.
I hope this helps,