A rental inventory gives full details of the condition of your property and its contents, at the start of any new tenancy. It outlines not only the number of items in the property but also their condition.
It's advisable to have an inventory so that when tenants move out at the end of their tenancy period, you or your agent can refer to the inventory to check that everything is present and correct.
You can then submit inventory evidence if you raise an end of tenancy charge that your tenants choose to dispute and send on to the Independent Dispute Resolution service. Without such evidence, it's much harder to prove your case.
Be sure to draw up a fresh inventory before every new tenancy begins so that all information is correct and up to date.