In-place elements are custom elements that you create in the context of a project.
Create an in-place element when your project needs unique geometry that you do not expect to reuse or geometry that must maintain one or more relationships to other project geometry.
You can create multiple in-place elements in your projects, and you can place copies of the same in-place element in your projects. Unlike system families and loadable families, however, you cannot duplicate in-place family types to create multiple types.
Although you can transfer or copy in-place elements between projects, you should do so only when necessary, because in-place elements can increase file size and degrade software performance.
Creating an in-place element involves many of the same Family Editor tools as creating a loadable family.