The Latin title by which this work is known in Europe is a corruption, probably of an Arabic name, and it has stuck so thoroughly that the original title is the one that needs introducing. In Arabic it is the Ghayat al-Hakim, the Goal of the Sage, and it is the most substantial surviving manual of astral magic from the medieval Islamic world.
David Pingree did the source-critical work. The compilation, put together in al-Andalus in roughly the tenth or eleventh century, draws on Harranian Sabian planetary religion, on Greek and Hellenistic astrological material transmitted through Arabic, on Indian sources, and on the Arabic hermetica. It is a synthesis of an already long tradition rather than a single author's system, and its attribution to the mathematician al-Majriti is not sustainable.
It entered Europe by a specific and documented route. It was translated into Castilian at the court of Alfonso X of Castile in the thirteenth century, as part of the same programme of translation that produced that court's astronomical tables, and a Latin version followed from the Castilian. This is why the book is in European libraries at all, and why Renaissance magicians could read it.
Its practical importance is that it supplies the operative half of a system whose theoretical half came from the Hermetic and Neoplatonic texts. The talismanic magic of the Renaissance, images engraved in specific metals at astrologically elected moments, with suffumigations and invocations matched to a planet, is substantially this book's procedure. Ficino's own cautious astral medicine draws on it. Agrippa uses it. Much of the material in later grimoires descends from it, generally without attribution.
There is a point about intellectual geography worth stating plainly. The standard narrative of Western esotericism runs from Egypt through Greece to Renaissance Italy, and this book does not fit that line. It is an Arabic work, compiled in Muslim Spain, drawing on Syrian, Indian and Greek sources, and it reached Europe because a Castilian king paid for translations. Removing it from the account would leave the practical tradition without its main technical source.