What ST1100 says is right. If you do an extreme (very steep) curve, there will be less visible contouring effect in 16-bits compared to 8-bits in the region of the steep part of the curve. But how often do we perform extreme curves on our images?
For normal photo editting, yes you will see differences in the histograms (combing effects) when you do it in 8-bits and 16-bits, this means image degradation in the images, but can our eyes notice any differences?
Can you tell any differences between a 7-bit grayscale image with an 8-bit grayscale image?
So like in photography, whether to edit in 8-bit or 16-bit depends on what you want. There will be a trade-off between processing time and final result. The question you have to ask is whether the improvement (in any from your eyes) is worth the additional computational processing? Saving in 16-bit for future usage may be advisable, but remember, not only would you take more processing power, you would need more hard-disk space as well!