Research by Gabriella, Have, Marielle et al. (2007) suggests that prolonged amino acid release from the gut is better for the body in the long term. So for long term health and muscle integrity i.e. potentially staving off the onset of Sarcopaenia (progressive muscle wastage in old age) and supporting general musculoskeletal health, a slowly absorbed Casein protein source may be of significant benefit.
Gabriella, A, M., Have, T., Marielle, P, K, J., Engelen., Yvette, C. L., Nicolaas, E, P, D. (2007). Absorption Kinetics of Amino Acids, Peptides, and Intact Proteins. International Journal of Sport Nutrition and Exercise Metabolism. S23-S36.