After a heavy session of weights in the gym its vital that you have a drink to replenish your body. After your workout its valuable consume proteins and carbs to start the regeneration process, training speeds up the digestion so drinking after exercise is necessary. All the hard work needs to be maintained, you do this buy protein and carb intake it helps as a replenish fuel, activate anabolism and rehydrate.
So remember to build muscle and maintain strength you need protein intake directly post workout. This will replenish all muscles worked on well and fast !