So when you knit on straight needles, if you want to get a nice, smooth stockinette fabric, you have to knit on the front side and then pearl on the wrong side of the fabric in order to get stockinette.
But in circular needles, you only have to knit around and around and around.
Obviously, there's no wrong side because you only knit on the front. There's no place to stop and turn, and so therefore, you never have to pearl because when you're knitting in the round, in order to get stockinette, that's what just comes out naturally when you knit stitch after stitch, round after round, you end up with a nice, smooth stockinette stitch without having to do anything else.
So circular needles are really ideal for when you want to get stockinette and you don't want to pearl.