When it comes to progress rest is just important as practice.  Even I when I really get into my practice can overdo it.  That is when the practice starts to impede progress.  When you first start training I would say that rest is most important because your body is weaker and more vulnerable to injury.  If you become sore, just wait until your body heals and practice some meditation or chi exercises.

Personally I tend to push the limits of my body and after a session I can feel worse, tighter, less flexible and the parts I worked on also feel tight and sore.  I find that once I wait a couple of days the work I did has a chance to set in and once I’m healed I realize that I am stronger, more flexible and made great progress.  You see this is why we need rest.

When you have been practicing for longer the body may not need as long to recover.  Also like I said you can switch up your work out to concentrate on certain parts of the body while others rest.  So be patient, practice hard and let your body rest and recover and come back stronger.