Hair naturally produces oil called sebum. The sebum provides a barrier to the hair and skin and also moisture. When hair is washed every single day, shampoo strips the hair of the natural oils which can result in very dry hair or the overproduction of sebum.
Even my hair stylist has commented that she doesn’t wash her hair every single day and instead uses a dry shampoo in between washes.
For in between days, you can use dry shampoo to keep the grease from building up. Personally, I go about 3-4 days between washes and use dry shampoo, as needed, in between wash days. The less you wash your hair, the easier it becomes to go a few days between washes as the oil production slows down.