If you happen to let your car insurance lapse then you will not be covered by the insurance if you were to get into an auto accident or if a cop pulls you over and you have to provide proof of insurance then the cop will run your insurance and see if it's lapsed.
If the car insurance is lapsed and you're not covered then you'll get a ticket for no insurance on the vehicle and have to go to court to fight the ticket.
But if you did not have insurance because you let the car insurance lapse then you will lose in court.
Also if you do not reinstate the car insurance soon after letting it lapse then the car insurance company may within a month or two completely cancel your auto insurance and may not want to sell you another auto insurance policy.
So it's important to keep your auto insurance current and avoid letting it lapse because it can cost you more money in the long run.