The most common reason for needing a copy of a part is to display multiple variables on the same geometry simultaneously. When you create a copy, a new Frame is also created and the copy is assigned to it (when you create multiple copies at the same time, a new frame is created for each new copy). Using the Frame feature, frames can be manipulated (for example, translated or rotated) independently. See Create and Manipulate Frames for more information.

Consider a part clone (see Clone a Part) instead of a part copy if memory is not an issue.