I can't think of many cons, I had Copper's done when I fist got him, He squeeked when they did it but as far as I could tell it didn't really bother him after that. It was not expensive and the reasurance it provides is priceless. If something happened and he was lost or taken
I would be able to prove that he is mine. Could you imagine knowing where your baby was but not being able to prove he/she belonged to you. Or if some nice person picked them up but when they scanned for a chip there was none to be found so you sweet baby never returns home, it happens, why chance it?