Paclo isn’t a pesticide, its actually whats called a “Plant Growth Regulator”. There are several different types, notably Giberellins and Giberellin Antagonists, of which Paclo is the latter. Its used on cannabis to reduce internodal spacing and give stouter stems. On other plants (Tomatos, peppers, ornamental flowers) its also able to cause early fruitset but I don’t believe it has the same effect on cannabis.
Basically, people use Paclo to bump up their yields by chemically improving their stack and the denseness of their bud.
Edit for clarity: Don’t use Plant growth regulators on cannabis because its really bad for end users, especially when extracted and concentrated. Hence when they’re usually marketed as an “Ornamental PGR”