Explanation
Stateful Inspection is a firewall technology that inspects both the header and the payload of each packet and keeps track of the state and context of each connection. Packet Filtering is a firewall technology that inspects only the header of each packet and does not keep track of the state or context of each connection. A benefit that Stateful Inspection offers over Packet Filtering is that only one rule is required for each connection, whereas Packet Filtering requires two rules for each connection (one for each direction). Stateful Inspection also offers other benefits over Packet Filtering, such as enhanced security, performance, and flexibility.
Stateful Inspection does not offer unlimited connections because of virtual memory usage, nor does it avoid using memory to record the protocol used by the connection.References: [Stateful Inspection], [Packet Filtering], [Firewall Technologies]