A 28 inch suitcase can be a practical choice for many 7- to 10-day trips, especially when you are packing several outfits, larger shoes, jackets, or other bulky items. The extra capacity also gives you more flexibility if your return trip includes shopping or souvenirs.
You may not need a suitcase this large if you pack lightly or have access to laundry. On the other hand, cold-weather travel, formal events, family packing, or trips involving different activities can quickly increase the amount of space you need. In those situations, a 28" case gives you more room without having to compress everything into a medium suitcase.