You bought the minimum coverage because it was cheap. Then you got in an accident and realized your liability limits are going to leave you personally responsible for the rest. Or your homeowner's policy has an exclusion you didn't know about until you tried to file a claim. The time to understand your coverage is not when you need it.
An independent insurance agent - vs. a captive agent who only sells one company's products - can shop your coverage across multiple carriers and actually find you better rates. They can also do a real coverage review: your umbrella policy, your auto liability limits against your net worth, whether your jewelry is actually covered.
Yearly reviews are worth doing, especially after life changes - new house, new car, marriage, kids, business income. Red flag: any agent who can't explain what's NOT covered by a policy, or who gets defensive when you ask about exclusions. The exclusions are where the policy actually matters.