It basically depends on what you want out of it. If you want to run close to the limits of your absolute best possible performance, be prepared to feel like sh@t immediately after finishing. I used to feel like I could not carry on if the finish straight was any longer, even by 20m, and my usual finish was to hit the line, carry on running rapidly decelerating, then find somewhere to lie down!
However, racing to your limits each time can become quite draining and also lead to you dreading the pain that is associated with racing, and really detract from your enjoyment, so I agree with Tony - you don't want to do this every race, only do it when you're trying for a PB.