A complete food has everything in it
Like a balanced meal, it has the right amount of fat, carbohydrate and protein and vitamins and minerals for health. It doesn't matter if it is a tin of complete food or a pouch or a portion of dried food the meal is essentially the same and nutritionally balanced.

So if you feed complete, complete, complete, then that is fine, but if you start adding complimentary foods eg chicken then you have raised the protein portion of the diet and so therefore the food is then unbalanced. The chicken although not bad for them doesn't contain the same amount of vitamins and minerals that the equivalent weight of the complete food has.

The feeding of treats and bits of chicken, prawns and the tin of Applaws will alter the balance of the food.