What is the disadvantages of insurance?

It costs money. You are basically betting against things going well. If you are a careful manager and have some cash reserves for emergencies your total cost may be lower without insurance.

Stated otherwise, in return for the payment of money (the insurance premium), the insurer assumes the financial risk of loss for a specified occurrence or occurrences. The range of occurrences and the amount of the financial risk is specified in the insurance policy.

Rather than purchasing insurance, one could "self-insure". That means that the person or entity could assess the likelihood of a loss occuring for which he/she/it may be found legally liable for damages. Further, an assessment would have to be made as to the amount of damages for which it could be held liable if found to be At Fault, and the cost of defending itself against the claim. It would also have to decide how much of its assets it is willing to place at risk to pay damages to the injured party if found liable.

If the amount of the insurance premium is more than the dollar amount that is at risk by self-insuring, it may make business sense to self-insure. If not, there is little, if any, risk to insuring against the risk.