If you don't, the result could be blisters, corns, calluses, and in extreme cases, even bunions. Different sports require different levels of support – hiking and running on a treadmill, for instance. Know what the requirements are for the sport in which you are going to be taking part.
Have your foot size measured every time, as foot size does not always remain the same. Most people's feet are slightly larger in the late afternoon to what they are in the morning.
Ask a podiatrist's advice when buying sports shoes. This could sort out many problems before they happen.