This study found that 20-40g of protein post-workout was more effective than 0 or 10g at increasing protein synthesis in trained individuals. If gaining muscle mass is your goal, adequate protein intake is incredibly important – consuming less than optimal amounts of protein can impair your muscle gains. Larger and more trained individuals may benefit from the higher end of the 20-40g spectrum, especially when considering long term gains.
Source: Witard, O. C., Jackman, S. R., Breen, L., Smith, K., Selby, A., & Tipton, K. D. (2013). Myofibrillar muscle protein synthesis rates subsequent to a meal in response to increasing doses of whey protein at rest and after resistance exercise. The American Journal of Clinical Nutrition, 99(1), 86-95.