Writing an enduring teen drama is one of the hardest TV feats to pull off. Right around season three or four, as the series leads are supposed to graduate, these shows usually stumble. The degree of difficulty on Smallville was even higher. How do you graduate your main character into a cape and tights instead of some unnamed Ivy League school? The answer ended up being rather complicated. The series pushed some canonical events to the forefront while leaving others for later in the series. One of the smartest moves the series made was having Clark leave the town of Smallville for Metropolis at the end of season two.
It's unusual to leave your titular locale so soon—imagine The Office outside the office or Cheers outside the bar. The creators understood that they if the show was going to enjoy a long run, they had to show audiences that the man who would be Superman was on his way to his destiny, that the show was going to bridge the gap between boyhood and Superman-hood. Forcing the march towards becoming Superman built up the good will that allowed Smallville to take eight more years to complete the journey.