There are five basic legal principles of insurance that must be seen to apply before the policy is valid - Insurable Interest, Indemnity, Umberrima Fides, Subrogation and Contribution.
Indemnity - This means that the insurer will reimburse the insured person to the extent of the loss sustained but no further.
The object of this principle is to prevent persons making a profit from insurance
Traditionally, most insurance policies, other that life assurance policies and personal accident, are contracts of indeminity. The advent of new-for-old policies challenges this principle in a limited way. The insurance industry justifies this limited nullification of this principle on the basis of economy of replacement, i.e. it is cheaper to simply replace certain items than go through the process of estimating, valueing and repairing these items.