We have had nearly zero blown head gaskets, and this collective forum has developed an opinion that re-torquing the head isn't necessary.
We have had several bikes that have developed small oil leaks when the oil "seeps" around in the layers off the head gasket. A passage at the right rear of the cylinder barrel supplies pressurized oil to the head, and that oil can creep between the layers of the head gasket and come out at the studs under the intake and exhaust port. Would re-torquing the head prevent/stop that...I dunno?
Also we have had several engines leak oil at the left front cylinder head washer.....the space around this stud has a passage for the oil to drain from the head back down to the crankcase. And we had one member whose right rear cylinder stud began to leak oil from the cam housing above....the nut and copper washer is in the cam housing and is exposed to the oil in the head, and if the copper washer doesn't seal it can drip oil out onto the head in the hollow space that goes through the right side of the head from the exhaust port back through the head.
If you have to take the head cover off to fix something like a leaky head plug, you need to re-seal the head cover to the head to fix a leak, or you are doing work to the cam or rockers - you might want to re-torque the head/cylinder studs. You need to remove the nut and copper washer, clean the area well, use a new copper washer or anneal and smooth the old one, apply a small amount of sealer to the bottom of the washer on the left front and right rear washers, apply never seize to the studs and nut.....then re-torque the head. I don't believe it is necessary to come back later and re-torque them.....once is enough as the torque value will not be the same once the fastener stops moving (static friction has to be overcome).
Re-torquing the head may help to stop the oil weeping around in the head gasket layers - maybe.
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