Why a suregrip?

ok i have a question. i have dealt with gm's for a long time. this is my first mopar i have ever had. in "GM" land no one wanted a "open" rear, with single wheel drive. you had to have a "posi" unit in it. it seems that with mopar everybody is always asking if you have a "suregrip" in it. it "seems" to be the rear of choice.just why is the "suregrip" rear so good? it is single wheel drive too....i could be wrong about all this, but am i?