Well if you think of a material like say plain wood, it doesnt have much spec so using a blin you would alter the settings to suit, if its say galss, again using a blin you would alther the spec roll off etc etc to suit the material.

Theres a great texturing articl by leigh van der byl, heres the link

https://www.leighvanderbyl.com/tutorials.html

have a look in the articles section, should give a better description of the material properties and how they realye to real worls materials.