The primary purpose of a rental inspection is to confirm the condition of a rental unit at a particular point during the rental process.
When inspections are done before move-in, the rental inspection is done to get an idea of what condition the property is in before the tenant occupies it.
When inspections are done mid-lease, the rental inspection is done to ensure that the property is being properly maintained and there have not been any excessive damages done to it.
When inspections are done at the end of a lease period, the rental inspection is done to verify that there are no damages beyond normal wear and tear, before the security deposit is returned.