I am trying to figure out the difference between uniting with the pathfinder tool and making something into a compound shape which is an option on the pathfinder tab section. I know with unite you can get shapes into one but what is the point of compounding it to a shape and then expanding? Isn't it the same?
The Pathfinder Panel, by default, creates altered objects and then expands them. You can hold the option/Alt key down when clicking a panel button and the shapes will not be expanded (similar to using the Effects menu item).
Any pathfinder operation may or may not create a compound shape. It all depends upon the original artwork. If the artwork has areas where a "hole" is needed in the middle of other objects, then a compound shape is needed to ensure that "hole" acts as a proper counter.
The Pathfinder Panel menu item for
Make Compound Shape is exactly the same as holding down the option/Alt key and clicking the
Unite button on the panel or choosing
Effect > Pathfinder > Unite. All 3 of those commands do the same thing. They tell the objects to unite but not expand. This leaves the artwork in a "live" state so that individual objects can be moved or altered and the appearance remains as if they were united.
Note: in Illustrator CS3 or earlier the Option/alt key and Pathfinder operations acted in the exact opposite manner. Adobe reversed the operation commands in CS4.
Compound path will unite all selected shapes in a totally third shape while the compound shape preserve the selected shape for dynamic editing. that's mean you will be able to do any transformation operation to any element in the compound shape even after unite it.