A portrait crop can give a person or product more attention by removing unnecessary space at the sides. It can also remove context that makes the image useful. Look at the original before selecting the shape: a person holding a wide object or a group spread across a room may not fit into a narrow frame. The cropper cannot move those objects closer together.
This page starts with a 4:5 export at 1080 by 1350 pixels. Those dimensions are an example for the workflow, not a rule for every platform or gallery. Change them when the destination asks for something different. Exact output crops to the chosen ratio. If preserving the complete photograph is more important than obtaining a portrait-shaped file, choose Fit within and accept its original proportions instead. No background extension or border padding is added here.