What is the difference between .save() and .insert() in the Repository when wanting to create a new record?

In the code, the comment for .insert() is:

// From https://github.com/typeorm/typeorm/blob/b6c828cc6c9786c155165d97e1f21af7cf423075/src/repository/Repository.ts#L224-L232


    /**
     * Inserts a given entity into the database.
     * Unlike save method executes a primitive operation without cascades, relations and other operations included.
     * Executes fast and efficient INSERT query.
     * Does not check if entity exist in the database, so query will fail if duplicate entity is being inserted.
     */
    insert(entity: QueryDeepPartialEntity<Entity>|(QueryDeepPartialEntity<Entity>[])): Promise<InsertResult> {
        return this.manager.insert(this.metadata.target as any, entity);
    }

In the code, the comment for .save() is:

// From https://github.com/typeorm/typeorm/blob/b6c828cc6c9786c155165d97e1f21af7cf423075/src/repository/Repository.ts#L140-L151

    /**
     * Saves a given entity in the database.
     * If entity does not exist in the database then inserts, otherwise updates.
     */
    save<T extends DeepPartial<Entity>>(entity: T, options?: SaveOptions): Promise<T & Entity>;

    /**
     * Saves one or many given entities.
     */
    save<T extends DeepPartial<Entity>>(entityOrEntities: T|T[], options?: SaveOptions): Promise<T|T[]> {
        return this.manager.save<Entity, T>(this.metadata.target as any, entityOrEntities as any, options);
    }

I don't understand what does:

Unlike save method executes a primitive operation without cascades, relations and other operations included.

From .insert() comment

means