Why planets and stars are always round/oval in size? What kind of stability it provides to each and every celestial body that each one them are round in shape?
The gravitational is radial only. That means if you tried a different shape then you would have regions, like hills, where a change in the angle would experience a much less attraction towards the center. This region would, over time, be attracted to a different angle with a greater force of attraction. Or spherical. This results in a spherical-like shape.