Insurance companies want to know of any eligible drivers in your household, including your spouse and any dependents of legal driving age. You do not have to list all family members as drivers on the car, and have the option of listing any particular individual as excluded from using the car. It is not always in your best interest to list your spouse as a driver of the car, but you have to go farther than leaving their name off the insurance, you have to have you spouse excluded from use of the vehicle.
For insurance companies, any person in your household with a driver license is a potential user of the vehicle. In this way, they are better able to protect you and to estimate the cost of you coverage based on who can be expected to drive the car. You are allowed to specify which individuals will actually use the car, but anyone who is not authorized has to be excluded from coverage. For a spouse with a poor driving record, this can save you a great deal of money on insurance premiums.
The problem is, if your spouse is excluded from using the car and an emergency makes doing so necessary, any accidents or other claims occurring while your spouse is under control of the vehicle would not be covered by your insurance policy. This means that you would be responsible for paying the full cost of the accident, including injuries, damages, and any potential litigation.
Unless there is no situation where your spouse would drive the car, it is best to list him or her as a driver on the vehicle. You may have to pay higher premiums, but the alternative could be a situation where you have to pay a lot more than the increased premiums would ever amount to. It is not enough to think that you each have separate vehicles, because you never know what the future could bring.