My instructions from over a decade ago was 1/6th of a turn past hand-tight. So one face of the nut would move right to where the face ahead of it was. I never questioned it. Wrenching a fitting tight not only cuts down on leakage and ingress, but it also preserves the ground path along the shield. A loose connection can also become a high resistance connection as well.
The other rule of thumb was if the customer owned it, we didn't wrench on to it. So cable boxes were to be wrench tight but a VCR wasn't. I hate when bastids do just that. I hand the wrench to the customer in those situations. DISH doesn't want the fittings wrench tight on their IRDs because those things are just soldered on there. The barrel nuts on them are like tits on Rosie O'Donnell, EFFIN USELESS! I don't know what DirecTV's specs are on their IRDs, but I do know they are built by the low bidder.