In Nature, carnivores have a diet that consists of many different protein and food sources. This serves a few major purposes. A varied diet helps to supply the full range of nutritional needs. A varied diet also helps to minimize competition with other carnivores thus increasing chances of survival. Lastly, a varied diet helps to stave of extinction should any of the food sources become unavailable. How healthy is a species if it has to rely solely on one food source? Therefor, nature has already equipped a cat's digestive system to handle various different food sources.
I, personally, use multiple different brands of both wet and dry food and even offer multiple bowls with those different brands at the same time. I feel that companies that make cat food do so in a particular way that may render some nutritional gaps. By alternating brands or using multiple brands simultaneously, you decrease nutritional gaps by overlapping. Where one brand may fall short in a particular ingredient, another brand will not and vice versa.
This methodology of using multiple brands can also serve another useful function, preventing food allergies. While it is hard to believe that a carnivore can in fact become allergic to particular protein sources, such as Chicken, it is happening with more frequency then you'd believe. I feel that food allergies are the result of the push by food companies to not switch brands and also by food companies relying solely on the same protein sources. Being exposed to the same protein for extended periods of time has in fact been shown to cause food allergies. Of course, the pet food companies can again profit from this as well by selling "hypoallergenic food" diets at top dollar.
Best solution to prevent food allergies is to use pet food that has different protein sources. What can be deceiving is pet food that is marketed as having one protein source will often also have another cheaper protein source as well. Chicken is the most common protein allergy in cats because they put it in almost everything. Even food that says "turkey" will have chicken in it. Read the ingredients list on your pet food to see this point. "Limited ingredient diets" were designed to combat this by offering a single source protein. While you do not always need to use limited ingredient diets to prevent food allergies, it is something to be mindful of. At Lap Leopard Bengals, we use single protein sources that include: Pheasant, Turkey, Buffalo, Rabbit, Lamb, Venison, and Duck.