An easy assumption is that the larger the state, the more likely it is to have mnerals, energy supplies, fertile soil, etc.,from which it can benefit. Generally that's true, but much depends upon the accident of location. Australia, Canada, Russia are all huge but they have relatively small areas capable of producing agriculture, so great size can be a disadvantage. A large country may have vast unoccupied areas that are sparsely populated. These areas are difficult to integrate into the mainstream of the economy and society.
Small states are more likely to have a culturally homogenous population.
The smaller countries find it easier to develop transportation and communication systems to lionk the country together. They also have shorter boundaries to defend against invasion. Size alone is not critical in determining a country's stability and strength, but it is a contributing factor. The ideal shape could be a circle with the capital city at the bulls eye in the middle. The compact shape is beneficial.