The iAd Producer default setting "Copy files to iTunes media folder when adding to library" can lead to an extremely large iTunes library file. Before developing iTunes LP and iTunes Extras using iAd Producer, deselect the checkbox to "Copy files to iTunes media folder when adding to library." This checkbox is located in the Advanced tab of iTunes Preferences.
iAd Producer 4: Settings for iTunes LP/Extras development
Learn more about iTunes settings for iAd Producer 4 when developing iTunes LP and iTunes Extras widget project types.