[rules-users] Stateful Session

Can anyone explain to me why I would want to hold a reference to my working memory in the ruleBase? The way we use the rules in our application is that we load all the copiled packages at the begining (we have API in place to replace, remove or add packages in runtime). The users invoke operations on different objects that get evaluated by the rules. Each time we call onto our factory get the correspondiong rulebase and invoke 'newStatefulSession()'. If I understand this correctly each time we create a new WorkingMemory instance which will not be garbage collected when were done since there is a reference to it? What is the difference between Stateful and Stateless sessions? Is there a way to reuse working memory from a ruleBase? thnx