Pros: You can freeze or delete the bloat that you ordinarily can't disable. If you are of a mind to, you can enable free tethering. You can install the CWM recovery that will allow you to clear the cache', make a backup of the phone, and install apps to the system area.
Cons: Voids the warranty, but if your phone is over a year old the warranty is up anyway. Performing some of the above tasks can brick your phone - which is why you make a back-up so hopefully you can restore it.
As far as call quality, it's terrible. I have hearing problems & to me it's so bad that I carry a flip phone on prepay so I can do business - interestingly enough a Casio Ravine 2. I rarely use it as a phone except when overseas. The call quality is much better on GSM than CDMA. I use it for email, quickly looking up parts and stuff on the internet, providing internet to my tablet and laptop computer, and to play music.