User blog comment:Thailog/Ep. 205 "Beneath" discussion/@comment-432124-20120526204619/@comment-432124-20120527210603

So you think that nothing in those episodes are important to the main plot in later episodes. Okay let's see here.

1. "Denial" introduces us to Klarion and Doctor Fate, both important to the main plot and to the development of the characters (i.e. Klarion is a member of the Light who is controlling the League in "Auld Acquaintance", Zatanna's loss of her father to Doctor Fate is what puts her on the Team in "Misplaced" and she was the one who detected the magic of the Starro-tech in "Auld Acquaintance".)

2. "Failsafe" - Where do you think the Team got the preparation for this alien invasion? Plus, the trauma from that episode results in the intense therapy sessions in "Disordered", which in said episode, pushes Superboy to run off and discover the Apokoliptian tech that becomes important in "Image" and "Usual Suspects".

3. "Secrets" - It may be the most fillerish episode, but the mole conversation in that episode becomes important later on.

4. "Coldhearted" - The involvement of the ice villains in the Ice Fortress thing combined with Professor Ivo's involvement in "Insecurity" is what makes everyone suspicious about Hugo Strange's involvement in all the criminal activity which is confirmed to everyone in "Usual Suspects".

5. "Performance" - Here, we get a good look at Superboy's Shield addictions and his "roid rages", the guilt of which is what likely causes him to confess his secrets in "Usual Suspects".

So no, none of these episodes are truly filler episodes and everyone of them has some detail that affects the main plot.