When to use water pressure regulator on fiver?

Here is a question.. they say that the regulators max the pressure at 40-45 psi.... what is the safe max pressure ? according to the video I just watched by Valterra.. the old trailers are rated at 45-45psi... and the newer trailers are rated for 100psi but they recommend no more than 60 psi....?? mine is adjustable and being of the older school of thought... I set it at 40...with low water pressure