A review should be done periodically. Once a year might be appropriate for many businesses. Many insurance premiums come due or up for reevaluation annually. That would be a good time to consider any changes in your risk analysis. You should also consider a review whenever you business:
1. gets larger or smaller
2. changes its nature as when it diversifies into new businesses or markets or products
3. relocates
4. anytime your business evolves in any way that could change your risk profile.