What are all the benefits of having a PCL reconstruction surgery vs just leaving it alone?

Quite variable. A PCL partially heals in a slightly looser position. Some patients have minimal difficulty with a PCL tear while others have instability sensations and weak push-off strength. Still others have rotational instability. Because of this, the PCL discussion needs to be personalized to your specific situation. This should really be addressed with a PCL sports medicine specialist.
Up to You. As the posterior cruciate ligament PCL treatment is some what controversial, PCL (along with other ligaments) keep joint stable, resists tibia being pushed posteriorly, femur sliding anteriorly, after PCL repair will have less pain, swelling heal faster than non operated patients and go to full activity quicker.