Often times riders just accept whatever their bike comes with. Whether you have bar ends or not, read on to learn when you should or shouldn't have them. Promote a better climbing position. Allows for easier breathing by opeining up your upper body. Some models can protect your hands from branches when riding.
Helps prevent fatigue by offering more hand positions.
If you have a carbon fiber bar, you could risk crusshing or cracking it. Most models take up an inch of your handle bar space on each end. If you have wide shoulders, you may not like the squished in result. Increased risk of injury in a crash. A good place to start is to install them at 45 degrees.