Celebrity Judges: useful or not?

Here, the celebrity Judges include Preity Zinta/Kareena Kapoor/Malika Sherawat/Priyanka Chopra/Karan Johar/Sohail Kapoor(actor from movie Aryan)...and all those big hotshots..(not the recent music directors on march 6th's show)...because I think all they do is say "good luck", "good Job", "do better"..and even if a singer hasn't sung well at all, they don't give any negative remarks..which is nice but common---since they don't have too much experience in singing..obviously they won't really be able to critique the singers appropriately anyway, so why do they really come to indian idol, is it only to promote themselves because I don't think they quite know that much about music. Do u guys agree/don't agree?