I like LaRue’s answer.
If you are working with someone in the weight room presumably you have done some preliminary work to determine their static alignment and determined whether there are some misalignments or chronic imbalances. Depending on what you see when you look at the static base, and then how motion generates through the whole kinetic chain you may find that some stretching is warranted in particular areas.
That is why I like LaRue’s answer“. genetics and life history and fitness level all vary so much. How you might approach someone with a functional scoliosis will be somewhat different than how you would approach someone with no injury history and years of strength training.
As well to say ‘stretching’ is like saying ‘should you ever eat carbohydrates?’ That is a big category. There are huge differences between say PNF and static stretching, or myofascial release, and times and people where one or another may be helpful.