Most martial arts exist on the platform of "If this, then that."  When they are attacked like this, then they will act with that.  From this basis, one can see why almost all martial arts at their core contain sets of kata or predetermined and predefined movement.  One might be asking themselves "Why?" and "Isn't it fake then?"  The answer to both of those questions is yes and no.  It all comes down to learning or, rather, "How does one learn to act in any given situation?"

How we act is a function of pattern recognition.  Our brains recognize a pattern then act appropriately.  The brain has the uncanny ability to adapt to any situation.  It adapts based on similarities.  For instance when you are driving a car and someone cuts you off, the circumstance isn't the same as the last time nor did you train defensively to maneuver out of the way, but you steered out of harms way successfully nonetheless.  How did you do this?  Through imprinting.  All of ones driving experience and training becomes imprinted into their mind.  From there our minds take that imprinting and lay it over the current situation and hence you came out safe.  This is also why younger and newer drivers get into accidents far more often than older or more experienced drivers.

With the kata practice, the practitioners are trying to imprint scenarios into their minds so that they may act appropriately when they are confronted.  It won't be the same each time out but our minds are extremely capable of picking out the similarities and acting appropriately like when swerving out of the other car's path.  Also, all of this needs to be done in the blink of an eye.

To say that kata or form is meaning less is to not understand how human's learn.  From the moment we are born, we are copying down patterns of movement.  I don't think any baby came out of the womb walking or talking and thus needs a form to copy.  Based on this knowledge we can see that predefined movement is how we as humans learn and are thus able to act accordingly within a blink of an eye.