I've left mine connected but have had an issue with re-connecting a couple of times.
It usually send to be when I've been connected and then removed the Android phone (Nexus 5) from the car & taken it out of Bluetooth range with Torque still "live". It wouldn't see the OBD2 reader next time I tried to use it then. Unplugged the OBD2 reader & refitted it and the phone connected up no problem.
Other than that, it's been great & faultless.