In additional to extra weight and length, there are reliability issues. A suppressor that is poorly matched to your firearm can possibly make it less reliable. Then there's additional cleaning, maintenance, and impossibility of obtaining parts to fix it yourself. Also, you have to be careful to use the right ammo for it to be effective.
Suppressors are cool. I would like to have one really good one dedicated to a specific pistol.....but one would be enough for me.