Depending on the size and the kind of welding you are doing, they can use a little more or less than a standard collet body setup. What they really do best is to provide better shielding out farther from the cup. So you can use more stickout with your tungsten. Also they can provide a larger shielded area for materials that need more shielding when cooling. This often comes at the expense of greater gas consumption. One downside is that they are larger in diameter so they can make the torch a little more bulky in very tight areas. They have their place along with a lot of other options. For some materials they are a must, while others not so big a deal. I tend to use them with mostly larger cup sizes, but not so much with smaller ones.
Long arc, short arc, heliarc and in-the-dark!