well, real world from actual medical studies it takes about .4g/lb or so up to a tops of .6/lb for heavily training athlete to maintain muscle mass. So say for a 200lb guy max he needs to maintain is 120g. If he takes in 200g, he's got 80 surplus grams of protein a day. Muscle tissue has approx 160g of protein in it. so he's got enough surplus protein there to add a pound every other day which even on a high anabolic cycle isn't likely (remember thats a pound of actual muscle, not weight).
All the amino acids other than Leucine and Lysine are gluconeogenic - they can be converted into glucose. If you are taking in more protein than maintenance plus what your body is using to build more muscle tissue, it just gets converted into glucose as if it were carbs to begin with.
So its not really a waste, just that the extra pound of beef costs more than a pound of cooked brown rice so if money is an issue its not worth it to eat more protein than that, particularly using shakes (as since they digest so fast they tend to give a pretty big insulin spike as they get converted into glucose).