The primary advantage of Bentham and Hookers classification is

The correct option is: The taxa description is based on the actual examination of the specimens

Explanation:
The classification system proposed by George Bentham and Joseph Dalton Hooker is a outstanding natural system of classification for seed plants (phanerogams). One of the most significant and practical advantages of this system is that it was not merely compiled from existing literature or theoretical models. Instead, the description of each taxon (family, genus, and species) was written down after the direct, careful, and actual examination of original plant specimens (mostly herbarium sheets and living plants available at the Royal Botanic Gardens, Kew).
Because the classification was based on firsthand, empirical observation of specimens rather than second-hand accounts, the keys and descriptions are highly accurate, reliable, and exceptionally useful for practical plant identification and herbarium organization.