If you are occasionally dabbling into different sports, then you may just need a cross trainer.  However if you are specializing in a sport or training, then you should get a shoe specific for that sport.  For example, if you are a runner, then a running shoe is superior to a cross trainer.  The is because a running shoe has extra padding in the forefoot and the heel for high impact.  On the other hand, if you are an avid tennis or volleyball player, you want a court shoe that has extra stability for medial and lateral movement and quick starts and stops. So it is worth looking into getting the proper gym shoe for your particular sport both for better performance and to prevent injuries.