Its an "over center" spring, meaning it will pull either way once it goes past "center. So ... when you depress the clutch it goes past center and helps your left foot overcome the pressure plate. When you release the clutch and the pedal comes back up (from the force of the pressure plate) it once again goes past center this time bringing the pedal all the way up.

Its just my thought but leaving this spring out would mean that the pedal would only come up as far as the pressure plate pushes it. This would leave the release bearing in constant contact with the fingers and it would be continuously spinning. This can't be good. The itty-bitty spring on the fork is there to avoid this but it doesn't have the balls to do the job without the over center spring doing its job.