I just saw my med doctor and she mentioned switching me from IR Xanax (alprazolam) to ER Xanax (alprazolam), what would be the difference?

Convenience. The ER form has a longer duration of action, so, you take it less often. Also, prolongation of action can eventuate in more consistent serum levels, so ups and downs of activity are blunted, and you get a smoother end result, with potentially less side effects.