If you and/or the claims administrator disagree with what the treating doctor says or other medical issues then a doctor has to address those disagreements. You could disagree over:
Whether or not your injury was caused by your work
Whether or not you need treatment for your injury
What type of treatment is appropriate
Whether or not you need to stay home from work to recover from a permanent disability rating.
The QME (or AME if you're represented by an attorney) report will help determine what benefits you receive.