The use of lubrication on bolted joints is massively misunderstood and therefore underutilised.  A common miss conception is that lubrication on a fastener will allow it to come undone quicker.  The logic behind this being that the easier it is to run down the thread then the easier it will be to run off the thread.  This is true if the fastener does come loose but the effects of lubrication should be that this is never the case especially when used with the right securing device.

When applying “Torque” to a joint you should always be mind full that the Torque is simply a measurement of the rotational effort/force needed to turn the nut or bolt.  If you are trying to tighten up a nut and bolt connection that is dry then you will need more effort than you would need for the same bolted joint that has lubricant on.  

The frictional values are lower so you can get “more for less” but the most interesting part and essential for critical bolted joints is the level of consistency you get using lubricant compared to without.  A dry bolted joint will give you lots of variation on the Pre-load (Clamp Load) that you achieve for the same Torque value whereas when using lubricant, you will get a much more consistent value for less effort.  The table below shows some tests performed on various dry and lubricated joints.