Protect from rust
Sharp edges should be rounded
All painting systems whether it be wet paint or powder coating are more vulnerable on sharp edges because at these points it is usually a thinner coat. On the picture the fabricator has removed the sharp edges on the end of this balcony. A large radius is not required as long as the paint film is uniform thickness, which is not possible on a knife-edge.
The bottom edge is more likely to go rusty
The viscosity of water allowing it to form drips, along with it flowing to the lowest point, and invariably because it is not in the sun means the bottom edge of the steelwork is wet longer. If it is wet, it is more vulnerable to corrosion. Stair treads are often cut with a guillotine leaving a sharp edge on the most vulnerable area of the tread.
Water traps encourage corrosion
As with the picture shown, if it is wet, it is more vulnerable to corrosion. This balcony platform has been manufactured with a water trap. It will stay wet for most of its life. To make matters worse it will have a square foot plate from a post bolted on to it. This will mean the water will be sandwiched between two plates. A bad situation for a structural fixing. Place a layer of sealant between the two surfaces, even thick grease will last many years ,repelling the water.