Yes, there are times when immobilization is helpful and a good idea. If you break your arm it's a good idea to get a cast to protect your arm as it heals. If you severely sprain your ankle it can be helpful to wear an ankle brace for a week or two. But most immobilization we experience is not that type, but rather body casts that we don't even think about. Anything that limits joint movement is a body cast and will have negative effects on the body.
Here are examples of things that cast or hold the body in a certain position or limit movement: