The module is capable of separating a consciousness from the body and storing it in the module. The module is programmed with some fail-safe program that prevents the transfer of consciousness into another living body. However, the fail-safe program may be overwritten if the original host's body is dead. A person undertaking a long journey without proper storage of their consciousness would arrive at their destination as a fraction of themselves.
The Talthuns created memory modules for use aboard the Stromos and its two sister ships after they learned how their homeworld would perish. They knew that their awareness would not survive the long trip in stasis without the use of the module.
In 1991, when the Stromos crashed on P2A-347, some of the conscious-less bodies perished, and Pharrin transferred their consciousnesses into his own consciousness. Twelve years later, when SG-1 explored the ship, he stunned them and managed to transfer a dozen minds into Daniel Jackson. After some negotiation, however, Pharrin agreed to transfer their consciousnesses out of Jackson and into himself through the use of a memory module. (SG1: "Lifeboat")