When you grab onto bars ends while climbing, you're applying torque through the handle bars to the bike which pushes the rear tire into the ground for better traction on steeps. I had them for several years until I decided they were more of a distraction than they were worth. The same effect can be achieved by rotating your hands forward on the bars, gripping down tightly, and then trying to twist the handle bars toward you to apply the same torque. If you do this as you approach a really steep climb and get low and forward on the bike (nose of the seat in your crack) you will be able to climb anything without needing bar ends.