There are two types of application pools in Plesk: shared and dedicated. Shared application pools are assigned to serve sites that do not have dedicated pools. Dedicated pools are used to serve only the sites of the customer or reseller to whom the pool is assigned. Dedicated pools isolate sites of different customers or resellers from each other. It increases the stability of different sites if one of the customer’s or reseller’s sites crashes. For more information about application pools and their management see the Plesk Administrator’s Guide.