"In a science program on TV it was explained that if you grease nuts/bolts it can increase the torque by 20% I don't know if the mfg figures given are for greased or not.
Personally I use a telescopic wrench extended to undo them and closed to do them up, if you look at mfg supplied wheel wrench they are not that long so you don't over torque them. Cost in the UK £6, and yes I grease mine and never had any problems with warped discs!" - Ferkemall
Watch this answer as a video, right >>
I also have a very early how-to video on the correct tightening procedure to avoid warping the brake disc - how to tighten your nuts >>
This is, obviously, about wheel nuts and wheel studs. So, propeller-head time: Torque is applied to bolts/studs - whatever - to deliver clamping force by virtue of extension. Stretch. It makes sense that you get more extension from a particular torque application with the stud lubricated because there’s less friction opposing the application of the torque. And when a bolt stretches, it stretches elastically and thus delivers clamping force because it really wants to return to its original shape and size when you release the nut.
That happens up to a point - and after that, if you over-torque it, the deformation of that stud becomes partly plastic - which means part of it is permanent, and that reduces the clamping force despite delivering more stretch. You really want to avoid that.
Therefore, if the manual says - do not use lubricant - then, don’t. I am, however, a big of a fan of light lube on wheel studs and nut mating faces generally because it prevents them seizing up and being impossible to undo when you get a flat tyre at the roadside, especially when you’re using the joke of a lug wrench in most standard toolkits.