A high quality diet makes a huge difference. Beyond litter box issues, shedding and hairballs. There are going to be less trips to the vet, better dental health, lessened likelihood of kidney problems later in life, the list goes on and on.
On a side note; Purina, Iams and Eukanuba are NOT high quality diets. Vets are brainwashed by these companies in vet school and very few actually educate themselves on proper pet nutrition. They're also given incentives to recommend and sell these products, so they are rarely impartial. Read the ingredients on the back of the bag. If any of the first 3 ingredients is anything other than a protien source, find another brand. Cats (and dogs) don't need corn, wheat, rice or any other carbohydrate they stick in there as fillers.
You also want to watch out for "by-products" of the protein source. The nutritional value tends to be extremely low.