I agree mh many injuries do heal on their own, however choose not to immobilise by splint or cast a long broken/functional bone then you run the risk of that bone shifting and falling out of alignment, it will heal in most cases, but at what deformity? Remember bone is a living tissue and is constantly remodelling itself, this is for both children and adults.

Look at someone who has fractured their clavicle or scapula, run your finger along that bone and in the majority of cases you will feel a deformity if you don't see it first.

The lower arm has 2 long bones the radius and ulna which run parallel to each other, (The most common fracture is a distal radius or wrist) now if you broke your radius and decided to treat it without immobilisation you run the risk of being unable to use that arm functionally as the two bones work together, if they didn't you may lose the ability to pronate the forearm, as to do this the lower end of the radius needs to cross over the ulna, the radius enables the hand to turn when this movement is carried out. And lets not forget the nerve supply that could also become damaged (especially in open fractures)

Generally what a patient can expect is:

•Removal of cast at about six weeks.

•Some patients may start physiotherapy, if their doctor feels it is needed, within a few days to weeks after surgery, or right after the last cast is taken off. Especially if wrist or elbow movement is affected.

•Most patients will be able to resume light activities, such as swimming or exercising the lower body in the gym, within a month or two after the cast is taken off.

•Most patients can resume vigorous physical activities, such as skiing or football, between three and six months after the injury.

•Recovery should be expected to take at least a year. Some pain with vigorous activities may be expected for about that long.

I've worked in orthopaedics for the last 5/6 years and have never known a patient decline intervention as they would prefer to say a prayer... I wish they would, it would make work a whole lot easier ;)
(I worked with adults admitted through trauma or electively to correct a deformity)

K :)