Overhead and Profit, or O&P is a known expense that all contractors charge.  It is intended to cover the overhead / operating costs of a general contractor as well as the amount of profit that the general contractor typically receives, usually at a rate of 10% (overhead costs) and 10% (profit) which is added to the scope of loss.
As a rule of thumb, nearly all insurance providers will not hesitate to pay O&P when the project's scope of loss requires the application of three (3) or more separate trade entities; whereby the complexity of the project necessitates a skilled management of all labor and material deliverables to properly execute the entire project scope.