>>309523346
>>309524946
id mask just lets you premask different areas of the model in the modelling program so you don't have to redifine what those areas are in the painting program 
so basically it lets you define the glass parts, the metal parts, the fabric parts, the decal areas etc of the model in blender/maya and then have it load in already so you just need to drag and drop your smart materials onto those areas or start working on those masked areas without having to manually make the masks