In 'Business Rules' it is currently possible to show or hide a field based on the value of another field.
However, it would be very useful to be able to show or hide an entire tab or a sub-grid, based upon a field value. For example, a 'Order History' tab would be hidden if there were no previous orders. Or a category field shows or hides a tab based upon the selection.
This would greatly improve the UI and data entry in my opinion.