Think of this policy as your base layer of insurance, the starting point for complete coverage. It often combines coverage for business property and buildings, crime, and general liabilities, making it convenient, and often, more affordable than buying the coverages separately.
BOP is generally a great tool for small-to-medium-sized businesses.
This article by Trusted Choice explains the premise of BOP nicely and outlines other details business owners (particularly small-business owners) need to know as they look to fill their insurance needs: https://www.trustedchoice.com/small-business-insurance/