It was the basic system that the samurai trained in and was the fundamental requirement to qualify them in the Way of the warrior. Throwing, joint locking, strikes, kicking are part of the techniques that made the samurai so efficient. In some ways anything goes in jujitsu. There are many styles to choose from depending on the teachers background. The more traditional could quite easily have a very strong judo background.
Some schools have a history that can be traced back to several hundred years.
The training is very physical and demanding while most systems can be a very powerful and therefore makes an efficient modern self-defense system for practical application.