What's the point of roasting a whole chicken?

The reasons people still roast whole birds are:

• Roasting a whole chicken is easier than butterflying it. While it's not tough to butterfly a chicken many people don't know how, or don't want the cleanup
• It's less prep time to roast a whole chicken. If you are busy you can have it from the fridge to the oven in less than a minute, while butterflying or jointing it isn't super-quick
• Aesthetics: some people like the look of a whole chicken on the table

If your goal is to cook your chicken relatively quickly, the only reason to keep it whole is for presentation/appearance and to avoid cutting it up. (For example, I know some people who simply hate handling raw meat, and I imagine for them that the task of butterflying is not only laborious but distressing.) From my perspective, you can save so much roasting time by investing a couple minutes in cutting it up -- and it really only takes a couple minutes once you know how -- and get better evenness and get better crispness. Why not butterfly or cut directly into quarters or pieces?

However, sometimes the goal is not saving the greatest amount of time. The question mentions aromatics and elements placed inside the cavity: those will have greater impact when roasting for a longer time at lower heat. But the even greater advantages for the whole bird come when you lower the temp even more and take a "low and slow" approach, as some people do. While the USDA doesn't approve this, many people roast their chickens (and other birds) at 250F or 225F or even 200F, for anywhere from a few hours to 8 hours or more. With extended roasting time, the meat and connective tissue softens, the fat renders beautifully, and you get an extremely tender and succulent texture, while any aromatics have time to be absorbed more fully.

If you cut up your chicken into parts or butterflied it before such a long roast, it could dry out, and you wouldn't have the moderating influence of the large structure to keep the interior relatively balanced. It's like the difference between cooking a steak and large roast of beef. Use the same logic for large hunks of poultry: If cooking fast and quick, cut up is better. If cooking low and slow, there are flavor, texture, and moisture benefits to keeping it whole.

Additionally to the other answers, you cannot rotisserie a flat bird, which to me, is a great way to cook chicken.

One word.

Stuffing.

You can make stuffing balls, or cook it in a ramekin - but it picks up the meat juice from the bird, and can also flavor the meat from the inside.

Cooking meats whole and on the bone gives a deeper flavour and thus I would rather cook poultry whole, including chicken.

Obviously it depends on the exact recipe you are using the meat in, but if you plan to serve the meat as-is, accompanied by side dishes and a sauce, you will definitely get a better flavour by roasting the bird whole and then carving off the meat. If you use the meat as filling for a pasta sauce or curry, don't bother and just use carved up fillets.

As for the cooking time argument: I find that things taste better when cooked for a longer time, slowly. Your meat becomes more infused with your spicing and due to thickness retains its moisture better.

The problem with the breasts cooking before the legs on a roast chicken has been solved a long time ago and does not require a lot of extra effort. I'm sure the process is described somewhere on this site, but have not yet looked for it.