I will be changing my wife's shocks and struts next week on her 2012 Outback. The service manual says not to tighten strut mounting nut until the car is on the ground. Do I really leave the nut that locks the cylinder to the mounting plate loose until the car is lowered?
You should leave them just about snug, if not just a little loose. If you tighten them before you put it on the ground, when you do get the car on the ground, there will be tension on the parts, which means it will wear quicker. So, leave them a little loose, then tighten once on the ground ... there's no worries about safety when doing so. It's not like its going to detach from the vehicle ... the nuts/bolts are still there.