Running has great benefits.
For people with bad knees, or weak limbs and joints, it is important to regularly strengthen the area, and build muscle around the injury prone area. For example with those with bad knees, do forward lunges, lift weights on your feet or ankles and do knee strengthening exercises - in most, the knee is the weakest joint, because people don't often remember to strengthen that area, but it is the most important joint to be cared for in running. Injuries of all kinds are easily healed by strengthening up the muscles, it is one main step in physiotherapy.
Keeping the legs strong is a good thing. It is excellent to do calf muscle strengthening as well, like calf lifts, and before running do stretches and loosen up the limbs to combat injuries.
I have really bad knees, due to constant knee injuries in sports in my past, but when i strengthen them and build up muscle tissue around them they are just fine, and the injuries heal itself as long as it is strong and has muscle holding it in place.

For running, if people have joint problems, the proper running shoes are necessary, to provide shock and bounce when your feet hit the ground. Alternatives, like running on grass, soft trails in a forest, a treadmill, or a track which has a soft surface are better than running on hard surfaces like pavement, as concrete is not always beneficial to the body for anyone, the impact can injure joints. It is important to look after the body!