Many younger renters are going back to parents. If they continue to pay rent, probably no problem.
But what happens if there is for example a leak, with nobody there to report it or fix it? Insurance may be invalid during long vacant spell. Tenant should notify landlord under terms of the lease if theproperty will be empty for a while, but they may not have done so. Tenant may claim to not have left, despite not having done so, but how does one prove that?