Body modifiers use the three-dimensional (3D) geometry of an object, such as a mass element or a mass group, to add to or subtract from a structural member. You can also use a body modifier to replace a structural member.
After you create a body modifier from an object, you can delete the original object. However, if you have created a complex object, such as a mass group comprising many mass elements, you may want to retain the object in the drawing until you are sure you have the results you want for the structural member.