What I see fairly often is people unwilling to get near the limits of the tyres for "safety" reasons. They think that if a tyre load rating is close to their working load or that they need to use a pressure close to that marked on the tyre is in some way dangerous. As the tyre manufacturer has incorporated safety margins in the values what they end up with is margins added to margins.
My tyres have 65 PSI marked on them and I am quite happy to get close to that, the only reason I would baulk within a couple of PSI is I don't really know how accurate my gauge is. Similarly with load factor, if you have too high a load factor above working load the tyre will not flex properly to put down a good footprint so traction would be reduced.