An objective-case pronoun would be the correct case if the pronoun functions as any type of object like a direct object, indirect object, or object of a preposition. In a direct object the pronoun receives the action. Sara punched him. Him receives the punch so him is a direct object in objective case. Another example would be Sara lived in the home of her. Lastly, an example of the objective pronoun used as an indirect object would be Kya gave him the gifts.
Answer: They should be used sparingly throughout the essay. If something is important enough to be in the sentence, it should be fully part of it. As always, make sure to check with your teacher or professor. Hope this helps!