Every good quality torque wrench or screwdriver I've ever owned or used has instructions to store at the lowest torque levels. However, if you pay for good tools they often are for a higher level of precision than you need. So a torque wrench for use in aviation (as I understand it) will be calibrated fairly frequently. Some assembly shops use torque wrenches or screwdrivers that don't even have the torque levels labeled: you use a calibrator to get it to the right torque and lock it.
I calibrate my wrenches against each other (a click-type with a beam-type, for example). Or I use a weight an a lever arm. But I don't ever recall my torque wrench not being within the accuracy I need.
So the point is, to be sure store at low torque settings, but if you store at high torques it may not affect the calibration.