An empty building is a bigger risk: no one notices a leak, and vandals and thieves have time. So the BPP form restricts coverage once a building has been vacant for a while. What counts as vacant depends on who the insured is.
Tenant: "building" means the rented unit or suite, and it is vacant when it does not contain enough business personal property to conduct customary operations.
Owner or general lessee: the test is square footage. The CDI outline calls a building vacant when 70 percent of the total square footage is not rented or used to conduct customary operations. The ISO form, as quoted by IRMI, states it the other way: at least 31 percent must be rented and used, or used by the owner, for customary operations.
After the building has been vacant for more than 60 consecutive days, the form pays nothing for vandalism, sprinkler leakage (unless the system was protected against freezing), building glass breakage, water damage, theft or attempted theft. Other covered causes, such as fire or windstorm, are still covered, but payment is reduced by 15 percent. California's standard fire policy in §2071 uses the same 60-consecutive-day line for vacancy or unoccupancy.
Example: a building has been vacant for 90 days when a covered fire causes $100,000 of damage. The fire is still covered, but the payment is reduced 15 percent to $85,000 (before the deductible). Had vandals done the damage instead, nothing would be paid.
The fix for a building the owner knows will sit empty is the vacancy permit endorsement. The CDI outline says that when it is added to a BPP coverage form, the vacancy exclusion is waived during the policy period.