You should not consider using any kind of artificial mulch. Besides all the good arguments above, the most common artificial mulch is shredded rubber. It's ugly, smells bad when the sun heats it up, doesn't insulate well due to the large air spaces around the pieces and as it settles into the soil it creates a mess you will wish you'd never begun.
Just like adding rocks as a mulch, why would you add something that in ordinary circumstances you would remove if you were planting a garden?