the problem with DL, is that you can lift far more weight doing them wrongly than in a safe manner, so every one, does them wrong
how far is a long run ? three miles good 23 miles bad
leg presses on a machine were your wedged between a fixed object and a heavy weight will allow you to move considerable weight but also take your knees out
crunches are complexly pointless, they do nothing useful at all, sit up are better except if you have your feet secured, in which case the bulk of the weight is being moved by your hip flexors, and what most people dont need are tighter hip flexors. if you cant do sit ups with your feet free then you cant do sit ups
stair lifts make you good at climbing stairs, which may come in useful i suppose
squats are like dead lifts, dont load the bar up with a silly amount ( and do them properly) and thy are ok, but who doesn't do that ?