I am wondering what is the difference in the frosting if using the meringue? I always just use extra Powder to thickin up the frosting. Just wondering??

Wilton is in business to sell product.
Wilton is one of the 1st to suggest adding it to icing, saying it helps it curst better. Well it doesn't really. What makes icings curst is the ratio of fat to sugar.
If you don't believe that, try making a recipe w/meringue in it; then make the same recipe, leaving the meringue out.
I think you will quickly find it makes no difference at all