I'm not sure if there are any particularities with DMMs, but overall that's a recommendation for the use of different HW, to better the performance of an application, so that it doesn't maintain a reference to a device that is not needed, and as a good programming practice, to ensure that your application closes all references it opens, LabVIEW would close them even if you don't but it is recommended that you do this yourself in your application.
