This is basically injury prevention stuff. So the focus is on strengthening the things which tend to get injured, ie the muscles and connective tissue which take a lot of stress in weightlifting.
Some don't do this at all; it's not entirely necessary. Others just dedicate a time after their workout to do whatever they want, with no program for it as such. Or you can program it, or just program parts to work on each day. It's mostly up to personal preference; it doesn't matter a huge amount.