I have a weldment that is symmetrical so I modeled only half and then mirrored. In the weldment are also some sheetmetal parts. There are lots of parts to mirror and I don't always get them all in the first go. If I try to go back and edit the mirror to catch the missing items I get the message, "Only one body may be selected in a sheetmetal part." Nuts now have to delete the mirror and start over again!