Seat covers perform many functions that we may not think that our cars need. For example, they: • Protect our factory seats from harsh UV rays. • Act as stain and water repellent. • And generally serve to keep our car seats in the best state possible.  All these reduce repair costs as well as help to retain high resale value for our trucks. So maybe while the word "necessary" isn't the right word, "recommended" may be a better choice of terms.