The roll cast is an absolute necessity to learn.
I can remember when I first started learning to cast a fly rod, I had all sorts of problems trying to position the line for a cast. Learning the roll cast makes it easy. Now when I am teaching someone new to fly fishing I always start with the roll cast. It is the easiest way to reposition the line for another type of cast. It is the easiest way to lift a sinking line, or weighted nymphs, up and onto the surface to cast. It is the easiest way to cast when there is no room for a back cast.
For a wonderful demonstration and tutorial of the roll cast see this video made by the Grand Dame of casting Joan Wulffe, now up on the excellent MidCurrent site. It is the best explanation and demonstration of the roll cast I have ever seen. As a footnote, if you still think power and strength are effective when casting, watch Joan probably in her mid-sixties, showing just how wrong that notion is.