Just like issues, risks are a given on projects. And the same as issues, risks need to be identified and documented. The risk register is used for this purpose. Identifying risks should start as soon as the project launches.
Risk is an uncertain event or condition that, if it occurs, has a positive or negative effect on one or more project objectives such as scope, schedule, cost, and quality. A risk may have one or more causes and if it occurs, it may have one or more impacts. Known risks are those that have been identified and analyzed, making it possible to plan responses for those risks.
Risks hopefully are identified prior to their occurrence. When a risk is identified then a risk response should be crafted. A risk response is how the project will deal with the risk when or if the risk occurs. A risk response could be a mitigation plan. Other risk responses are transfer, avoid, accept, or maybe enhance, if the risk is an opportunity.
Having a risk register will help the project be more successful because knowing what could potentially impact the project and having a plan to resolve the risk is your first line of defense.
Risk registers are also a good document for identifying lessons learned so that future projects will have a baseline to deal with potential risks.