Pads made to protect elbows and knees are essential in the effort to prevent injury without impeding training.
Most martial arts will result in elbow and knees hitting the floor or other objects with little to no padding. Slide-on sleeves with integrated padding that fit over the elbow or knee can go a long way in keeping injury from this kind of impact to a minimum. Let's face it, injuries interfere with training and that's never an objective. This type of protection must also not restrict movement and have a level of comfort so it doesn't hamper your training session.