As long as the drivers are listed on the policy there is coverage. It doesn’t matter who drives the car more often or less often. Only when someone is driving the car and not listed on the policy, or they are an excluded driver, is there a problem when a claim is filed.

Okay it really depends on the insurance policy, but here is a general answer that is correct in most cases.
Insurance, by state law, must cover any one you let drive your car. However, most insurance companies require you to pay for insurance for all the members of your household who drive the car. Thus, your insurance might not cover a member of your household who drives your car, if that person is not listed on the policy.

Insurance (at least in the U.S.) follows the car and is covered by any licensed driver with permission from the owner unless they are specifically exculded on the policy.