One of the common real reasons for wearing a corset is being involved in reenactment. Historic costumes designed to be worn with corsets just do not look right without. Even old dances are easier to dance and look better when the the dancers are wearing the right underpinnings.
Some people also wear orthopedic corsets for various back problems like scoliosis. The construction of those corsets is somewhat different than that of fetish or historic corsets, but most of the tips for wearing one still apply as they share the same stiffness and many are also laced.