Let me tell you a lesson I learned when I first start baking. It is definitely not cool to substitute margerine or shortening for butter. Why?
Butter has the best flavor of all! It definitely dominates the world of cooking fat. Butter also has a melting point that is between margerine and shortening. What does this mean? Butter leaves your cookies chewy but they still have a little puff in them. If you like your cookies pancake flat, try the cheaper option, margerine.
Margerine has a very low melting point, so when making cooking they will come out very flat and likely very chewy. For those of you who care, it may have less calories, but it has a high amount of trans fat. Personally, I have found margerine is good for creating a unique texture in a few things, like poundcake.
Shortening, or what I like to call the pretty white fat. I really like to use all vegetable shortening, and I only like to use the good stuff. I'm not always an ingredient snob, but I have to draw the line somewhere. Shortening has the highest melting point of the three fats. For this reason, your cooking will not flatten out much. They may even end up looking like the same ball you put in the oven. Shortening also gives cookies a crispy outsides and cakes a fluffy texture.
Shortening is great for pie crusts, it helps make them flaky. I also like to use shortening in snicker doodles to give them that crisp outer layer.
Shhh, don't tell I have also experimented with lard. I made a pie shell and it was delightful. So flakey and yet I still loved the flavor. Let's keep that a secret though cuz I usually like to keep things healthy-ish.