Trapping is a unique skill most famous in such styles as Wing Chun Kung Fu.
The skill of trapping is primarily developing the skill of sensitivity.
Sensitivity is not necessary to be a good fighter, but it is the higher skill that can help anyone take themselves to the next level.
Often times sensitivity is replaced by speed and or explosiveness.
Jeet Kune Do practitioners practice trapping with focus mitts. This is because Bruce Lee was very into Western Boxing, and he also was into full contact sparring, which he apparently did with some of the best fighters in North America of his time.
So the Wing Chun practitioners probably have the best sensitivity skills because of how much Chi Sao (Sticky Hands) practice they do.
Jeet Kune Do practitioners are more likely to have a better sense of trapping application because of the focus mitt training.
Both are important because if you want to be able to use your trapping in real life you should go study Jeet Kune Do, but then when you want to further your sensitivity skills you should go train with Wing Chun people.