This has probably been answered but I am feeling a little dense today. Is the Wilton recipe for buttercream crusting or non-crusting? Also when would you use one vs the other? Any advice is appreciated.

The Wilton recipe is a crusting buttercream.

you use a crusting recipe when you need to get the icing smooth either the melvira or viva or whatever way you like best. If you are using a non-crusting recipe it is more difficult to get smooth, some use a hot spatula. If you are covering your cake in fondant it doesn't make a difference if the icing is crusting or not really.