These decorative pot feet have several different uses. The first is that whatever pot, planter, urn or bowl they are used with, they add an extra degree of decoration and design to the finished planted up container. The extra height and simple design element that the feet bring to the combination set it off whether the pot is used singly on its own, or as part of a grouping of containers where the few extra inches in height that they give, make the pot stand out from the background.
But there is another and just as important use for the pot feet. Lifting the planter off the ground by even a few inches means there is room for air to circulate around and underneath the pot. This helps to keep the bottom of the pot dry in winter months, which helps to prevent frost damage. It also allows the compost to drain freely which has the benefit of creating a good growing environment for the plant inside.
Most circular pots require just 3 pot feet to give stability. Square pots or troughs will need 4 feet, one at each corner.