From the senders point of view, keeping a copy of that email can be important. For example, if the risk materialises, the original communicator can point to the email and say "I raised this with you months ago".
The proactive employee may wish to do more than just flag the issue. If it's something they can't solve themselves, the ability to track the issue is important, potentially reminding the employee to remind the manager of the issue.
This functionality could potentially be delivered via the "assigning a task" functionality discussed previously. However, there is a cultural barrier to both raising tasks for people, and managing upwards. Additionally, a risk or issue may better sit in a different class to tasks, as they may not be something that can actually be ticked off.