There's a few reasons you might want to use margarine instead of butter when baking: Perhaps you're vegan, or you just want to cut back on saturated fats in your diet (of which butter has plenty).
Margarine can be used as a substitute for butter in most cases. However, some are designed for spreading, and others are hard and designed for baking so always read the packaging before cooking ...
The baking margarine help the mixture to cream well without splitting and holds it firmer at room temperature than if only butter is used. Dan Lepard's buttercream is firm and easy to pipe and ...