Postmodernism scrutinizes the accepted ways of producing art and finds new ways to portray interesting things. Without this approach everyone would still be scratching stick men onto cave walls. In a world in which change happens so fast, it's useful and important to think in terms of what changes, why it changes, and how the change helps or hinders us. Having said that, and in the long run, post modernism is as irrelevant as any other “ism”, all of which had their own junk philosophies to contend with, what matters at the end of the day is the content of art and how society or an individual responds to it that matters. Sadly post modernism could have provoked a radical and revolutionary response to society but its adherents proved conservative, more interested in money and their careers to make any meaningful art. So unlike so many “isms” whose adherents created great works in spite of a particular ism´s junk philosophy, post modernism hasn´t produced many works of literature worth remembering. Postmodernism is not throwing a whole lot of weird stuff together and seeing what craziness happens. This, however, is what a lot of people, including artists, curators, critics, and journalists who all should know better, think it is, This "anything goes" postmodernism is what winds people up and makes them say 'That's not art!' as if there's something which art ought to be.
If you're into literary criticism, read on.