It might have have happened that some Shaikh told someone to recite the best of invocations (Laa ilaha ilallah) after Compulsory Prayers as a medicine but people have made it a routine. After every Compulsory Prayers you hear a boom of this incantation in every Mosque. This is not supposed to be the routine incantation at that occasion.
(Sitting (majlis) on Sunday, October 10, 2010)