Yeah, I think it obviously goes without saying that for anyone with any sort of health problems related to feet or legs, there are very specific (and variable) footwear requirements. Especially if you're talking about putting strain on a joint, it makes sense that an alteration from the natural posture could help.

For most people, very high heels (not Nordic clog height like Danskos) will do more damage than plain flats, but it always depends on the heel and the flat. Some heels do offer support (while also putting too much weight on the ball of the foot and shortening the achilles tendon). And many shoes that are nominally sneakers due to their soft rubber soles are not actually designed for any kind of athletics; there are whole brands that make "fashion sneakers" designed to look like athletic shoes but not intended to be comfortable, let alone good for walking or running! But athletic brands, like Puma, Nike, Reebok, Adidas, etc, elevate the heel higher than the toe in their running and walking shoes. I've read that that slight incline is actually less stressful on joints. (My Pumas are definitely more comfortable than Wax's Converse, but I still wear them less.)