In a healthy situation, the root of the tooth is not visible. When there is bone loss, the root of the tooth can be exposed. A soft tissue graft can be done to protect the tooth from further bone loss. When a tooth loses the bone around it, it can become mobile. If you lose too much bone you can lose the tooth.
A soft tissue graft can also be done to cover more of the root if there is a concern about how the tooth looks. The root is darker than the crown of the tooth which can be an esthetic concern for some people. If there is sensitivity of the root because of recession of the gums, a soft tissue graft is an option for helping with this.