First, the insecticide or herbicide label is the law. So the product you select for use should be used only on the type of livestock allowed by the label, and mixed and applied strictly in accordance with label directions. Failure to do so is not only breaking the law but deprives you of recourse from the supplier or manufacturer if the product causes injury or is ineffective. Of greater practical importance, applying an insecticide to an animal of a type not listed on the label may result in animal injury or death. Also, if the target insect is not listed on the label you can't expect the insecticide to control that pest.
Efficacy translates into economics.
The different formulations provide options for convenience as well as to enable them to be applied where and when they will give the best results. Before buying an insecticide, one should read the portion of the label that specifies how the product should be applied. The same product may be labeled for use in several ways. The dilution rate for premise applications is likely to be much more concentrated than that for direct application to livestock. Spraying livestock with a mixture prepared for treatment of barn walls may result in animal toxicosis or death.