Why and when should I use memory saver

[Hollum]

Hello! I am new to Langgraph so these questions may be silly but ya'll manage 🙏 I have created a simple graph where the LLM just asks questions. After five questions provided to the user it should end the conversation.

Every time the user sends an input i store the message in my postgres db (using prisma) and pass the message history to my graph. I initialise the graph with the previous history like the following snippet.

const awesomeFunction = (chatHistory: BaseMessage[], input: string) => {

...code

const GraphAnnotation = Annotation.Root({
    input: Annotation<string>(),
    chat_history: Annotation<BaseMessage[]>({
      reducer: messagesStateReducer,
      default: () => chatHistory, 
    }),
    context: Annotation<string>(), 
    answer: Annotation<string>(),
    questionCount: Annotation<number>({
      reducer: (state: number, update: number) => state + update,
      default: () => chatHistory.length, 
    }),
  });
}

I am having a hard time seeing the difference between this and using the memory saver/checkpoint-postgres. What benefits would I be missing?