Because, it FEELS like there is recoil so I find a spray with it more accuratly. But I hate how it does less damage, and as a resut, sometimes you miss out on a kill.
I usually keep it unsilenced. It loses some damage when you put a silencer on, and I also believe it lowers RoF a bit. It also feels more accurate unsilenced too.
I silence it for short- to mid-range and unsilence it to kill scouters. Leaving it unsilenced shows you on radar too much. Flash bangs aren't the only thing that blind enemies.