Straight forward is this....dogs have a ZERO nutritional requirement for carbohydrates, period. If fed a proper raw diet, one which does include meat, bones, fat, connective tissue, organs, glands, etc. requires nothing else nutritionally speaking. For those that cannot feed a PROPER prey model raw diet, supplementation should be provided to ensure everything that the dog is missing out on is being provided. Keep in mind that most people do not have access to true prey model raw.
If you were to make a spreadsheet and list each item in a true prey model diet, including glands that most do not have access to, and break down the nutrients in each, you will come up with a balanced diet for your dog. This, of course, is assuming the prey you are feeding has not been artificially pumped with steroids, antibiotics and has been fed a proper, natural diet that will not alter the natural nutrient balance within their body.
Bones are needed, no questions asked. If you choose to feed meat without bones and supplement with another source of calcium, your dog will miss out on important minerals and nutrients within the bone and bone marrow. Not to mention that they will miss out on the natural teeth cleaning and the nurturing of their natural instinct to chew. Weight bearing bones - one should be more cautious with these than non-weight bearing bones as they are harder. With an experienced chewer, one who breaks up the bones nicely prior to swallowing them, there is less concern. Weight bearing bones from larger animals, cows, deer, etc. most often are best left for recreational chewing.
Some people choose to add vegetables or fruits to make up for some of the nutrition lost by not being able to feed a true prey model diet. Fruits and vegetables are not what a dog is meant to digest, period. So much so that WE need to pre-process them in order for a dog to be able to utilize any of the nutrition in them. Doesn't that tell us something? Dogs in the wild do not have food processors or vegetable steamers and they certainly wouldn't know how to use them if they did. Rather than fruits and vegetables, or carbohydrate sources, I much prefer a natural supplement to round things out if it's needed.
The ideas behind going grain free are this: First, using potato or a similar carb source allows the manufacturer to be able to physically make the kibble using more meat protein. This is more of an equipment issue for production than anything. In turn, yes, you are able to feed your dog a dry diet that is a bit more appropriate than a grain laden kibble with minimal meat protein. Second, it allows you to get away from grains in general. Third, it gives the ability to feed less kibble than you would a typical grain inclusive diet. And fourth, stools, coat, skin, etc. tend to improve because of the above.
IMHO, having a grain free kibble that is not high in meat protein defeats the actual true benefit of feeding a "grain free" kibble. The highlight, IMO, of feeding a grain free kibble is giving consumers the ability to feed a bit more appropriately by having higher amounts of real meat protein. To me, a high carb, grain free kibble is no better than a high quality, grain inclusive kibble, with the exception that it opens up options for those with real grain allergies.