User blog comment:-blak-/Cody VS The Writers/@comment-3014969-20101123202134

In the only TDWT episode where Sierra was kinda... knocked out ("PicNic at Hanging Dork"), Cody actually DID something (both in-game and for the Gwen-Duncan storyline). This proves that Sierra was simply added to "fulfill" Cody's role in someway and when she's not around, Cody can be an "useful" character.

Btw, I agree: a few other characters were kinda "rushed" in this Season, and I was quite surprised of how soon LeShawna was eliminated (though this was done to show the audience how "evil" Alejandro can be).