Silencers add length weight, cost and bulk. On gas operated guns they can increase blow back through the chamber and into the shooter's face. If improperly mounted they degrade accuracy and can damage the firearm. I have yet to see any improvement in accuracy using mine and the largest velocity increase I have seen is 4 fps on my 22lr.
I make silencers as a hobby and think the noise and recoil reduction are well worth it.