Board Thread:Questions and Answers/@comment-7708862-20130402005255/@comment-957629-20130403173920

"could" threaten does not mean "if he releases it goes boom"!! Nobody is denying Yammy's destructive force however his attacks have been shown as mostly melee in that form and his Reiatsu was not as dense as Ulquiorra's, since nobody commented on it!! Yammy released, no big deal, he was still dwarfed by the size of Las Noches and none of his attacks were shown to be as destructive as Ulquiorra's blasts, Starrk's ceros/wolves, Barragan's Respira nor Harribel's tsunamis of water!!

And regardless, before Yammy releases he is still only Arrancar 10 he is only zero after releasing so his case is ambiguous!! And anyway Ulqiorra states that the gran rey cero and release are forbidden because they "could destroy" not that "they will destroy it"!! It is only natural that Aizen, who is quite vain and proud would not want his palace to be destroyed even a little, although Yammy still caused considerable destruction!! No where does it state that "release=boom"!!