Thousands of years of refinement have given each of us an innate sense of a pleasing hollow form.
The earliest tradition for Open Forms (where the opening is the largest diameter) must have been for gathering, mixing, preparing food. A Closed Form (opening smaller than largest diameter) adds mystery about what is inside. Since ancient times these forms in pottery and wood had the practical advantages of being spill resistant and easily capped.
Today's potters and turners are rediscovering and pushing the limits of this form, beyond practical use, and as an object to view.