Card sorting is a technique that was originally used in libraries to organize large quantities of information. Card sorting uses physical cards with words (or pictures or physical objects).  The cards are put on a big table and users are asked to group these cards into categories that make sense to them.  

This technique allows to understand how users group information but is a wrong approach to organize information in a user interface because:

  1. When users interact with computers, the optimal information organization is not necessarily logical. Information can be organized along: 1) frequency /importance of use;  2) sequence of task 3) logical group;  4) standards (ex: month of the years), 5) numerical or alphabetical order.
  2. When doing card sorting, people are not in a natural work context. When people are performing tasks in natural work context, the information is deeply embedded in the context of the task, and the brain works in context.  
  3. People may confuse items that belong to the same logical group but needs to be separated to prevent errors. For example, “flight schedule” and “flight status”.

Conclusion: Go out in the field. Do not to lose time with card sorting and instead uses techniques such as observation, prototypes and iterative tests with users.