It is important to remember that the Reimage repair is an extensive repair of your operating system. Once used, your operating system is returned to a working state. Over time and with ordinary PC use, you may need to use the repair again, and if used too frequently the effects may be lessened.
However, if you are experiencing any one of the issues that brought you to use Reimage in the first place, i.e. crashing, freezing, blue screens of death, etc., then feel free to run the Reimage repair again.