The deadlift is a very unique exercise. The deadlift is an exercise that will help strengthen the axial muscles and ligaments of the body, most notably the thighs, gluteal muscles, spinal erectors, and trapezius muscles. Many people think of the deadlift as solely a lower back exercise, which it is not entirely. The main muscles that initially create the drive to move the weight are the thighs and the gluteal muscles. The lower back really just transmits the forces between the lower body and the upper body, i.e. the Trapezius, Rhombi, etc. So the lower back will get a workout, but the deadlift is not isolating the lower back so to speak, in the movement. If someone wants a lower back exercise they would be better off doing Good Mornings instead.
The deadlift also relies on a principle called concentric contraction. Concentric contraction occurs when a muscle shortens in length and develops tension, i.e. the upward movement of the thighs during the deadlift. Also a powerlifter deadlift is different from a olympic weightlifter deadlift. The powerlifter will usually have his hips higher when they begin the pull unlike an olympic weightlifter. The olympic weightlifter will have their hips closer to parallel with the knees and this also reduces the shearing stress on the knees.
Now comes the question are they useful for the Olympic lifts? Well of course.Although anyone practicing the deadlift would do best to not use an overhand underhand grip when performing the lift. It would probably be most beneficial to the lifter to use their snatch or clean grip when performing the deadlift to help mimic the actual classic lifts. Of course, the lifter should also try to mimic the first portion of the classical lifts as much as possible when performing deadlifts. Also if the lifter is going to incorporate a deadlift in their workout it would be best to do so at the end of a workout instead of the beginning to prevent unnecessary fatigue on the lower back. It is up to the lifter to decide whether to do clean/snatch deadlifts or clean/snatch pulls instead. As far as rep choices go below 5 would be ideal, most would do best to stick with the 1-3 range. As for how many sets, that is best left to the lifter, but they should not do too many because lower back recovery does take a while. Overall, it is up to the lifter to experiment around with the set and reps and find a suitable place in their program to implement some sort of pull, whether it is an actual pull or a deadlift. Good luck with training.