From the back cover:
This Monster and Treasure Assortment (Levels One to Three) is one of a set and is designed as a playing aid for Dungeons & Dragons. By using the assortment lists, game judges can generate any number of appropriate monsters or treasure by simply rolling dice - thus saving time in play and preparation.
[The 'Levels One to Three' is an error on the back cover of the Level Seven to Nine set.]
From the front cover:
This set contains lists of 300 monsters, 300 treasures, treasure storage/guarding/hiding modes, and complete instructions for using the assortment to fill in partially stocked or newly encountered dungeon levels.
From the introduction:
This assortment of monsters and treasures by dungeon level is designed to answer two needs. first, the package provides the Dungeon Master with a ready matrix of encounters when his players are exploring a dungeon encountered in a Wilderness Adventure. Second, and more important, these assorted monsters and treasures are aimed at making the DM's task a lighter one when it comes to readying the major dungeon in which most of his players' Underworld adventures will take place