They offer protection when income changes. Most people don't have a guarantee that their income will never go down. Under a noncancellable insurance policy, even if someone's income goes down later in life–if they are totally disabled–the company will pay the total disability benefit originally placed in-force. With disability insurance, if your income decreases, your coverage will stay the same. If you got laid off from your office job and had to take up another work for lesser pay, you would still be able to keep your insurance with a noncancellable policy.