1. capacity: the diameter of a 7-inch plate is about 17.8 cm, while the diameter of an 8-inch plate is about 20.3 cm, so an 8-inch plate is larger than a 7-inch plate and can hold more food.

2. Practicality: 8-inch plate is more flexible in practical use. For example, an 8-inch plate can be used to hold fruits, bread and other foods, but a 7-inch plate cannot hold these foods.