The posted numbers are a design range which take a lot of factors and design targets into account. You'll find that there is a sweet spot for long tread life before a lot of negatives start to occur, and this sweet spot in many tires is more than the manufacturer posted limit. And a different sweet spot for handling, which is generally toward the mid or low end of a posted range. Do some Google searching and you can learn how to set these for your circumstances. And search right here for what people have found with various tires with various loads on the Tenere. What I use for long tire life commuting is not what I use for a fun weekend, especially if I may go off pavement.
At softer pressures, there is increased tread movement (squirm) against the pavement and the tire has less load capacity. Hence the tread wears faster. At higher pressures, there is less footprint, the tire rides harder, and things can quickly can get downright hazardous due to it not following pavement irregularities well and slipping in corners. This can be magnified riding on wet pavement.
