I can think of one or two members who do mix foods together, and I used to do that for my cats in the brief period that I fed them kibble. And for my cats, incidentally, it worked very well
The downsides to mixing are:
- you have twice or three times as much food 'open' at any one time, and it can go a little stale especially if you buy large bags or have only one animal
- If there's a problem with one of the ingredients, like an allergy develops over time, its much more difficult to identify the cause of the problem
- The dog still eats exactly the same meal all of the time. Yes, he's getting a wider range of proteins etc, but that's not quite the same as variety which is also about meals being different (different for his internal organs too, not just for his interest)
Well, those are the downsides. Rotating through different brands is a slightly better way to go, but IMO feeding a mixture of kibbles is still much better than constantly feeding one variety only.