Under section 62 of the Residential Tenancies Act only food and perishable goods may be discarded immediately by the landlord and all other items should be stored securely pending an application to the tenancy tribunal. The tribunal will then make an order either for the return of the goods to the tenant, or allow for the sale or disposal of the abandoned goods.
This is not ideal for the landlord as it costs time and money to go and store goods for a tenant that has left the property. Not only will you be responsible for looking after their household goods, you will also be responsible for cleaning the property and getting it ready to be tenanted again. This all adds up and ultimately will come out of your pocket until an order for claims against the tenant is processed by the Tenancy Tribunal.
The key message is that by getting a disposal order from the Tenancy Tribunal you are protected against any potential claim from an ex-tenant.