A space maintainer is a preventive tool that can be used to prevent space loss when a baby tooth is taken out early.
Space loss can happen when the teeth around the tooth that was removed tilt into a space and then do not allow the adult tooth to have enough room to come in. This can cause crowded teeth, and increases the need for braces later on.
By placing a space maintainer in the mouth, you can hold the space where the baby tooth was with a small wire and band. It does not replace the tooth like a "denture" tooth, but food does not get stuck into the spot where the wire is because the gum is smooth (once it heals after tooth removal), and it will be easy to clean it with a toothbrush like normal.
Most kids may find it uncomfortable at first, but then they get used to it and forget it's even there.
Its also like having "braces" in the sense that you shouldn't eat any sticky things like candy or gum or the spacer can get pulled out and need to be recemented.
The best time to take out the spacer is when the adult tooth is coming in. It is easily removed by your dentist without numbing or pain and the adult tooth can continue to come in properly!