Joe Lewis only learned basic traps, which he says by PREFERENCE that he prefers to just punch and kick. He also learned a more kickboxing style of JKD, similar to what most of the Los Angeles branch of JKD was doing, except Joe Lewis was probably the most talented one among them all. Bruce Lee taught Joe Lewis basic traps, but Joe Lewis still preferred punching and kicking. By preference, Joe Lewis said he feels that trapping is useless and he never trained much in that range BY preference. Once establishing that it is by preference, it means his JKD is different and doesn't focus much on it. However to other JKD fighters, it's very useful.
Joe Lewis pretty much knows most of the basics in JKD, and some advanced techniques such as broken rhythm and the mentality of a fighter. Joe Lewis has said that hand trapping has helped though in certain fights he had, and he even goes into depth on basic trapping in his JKD tape.
Personally for me as a JKD fighter, I wouldn't say it is useless, it's a useful tool to whip out and keep your opponent guessing. It also mixes in well with boxing. You can do 2-3 step trapping techniques if you have proper sensitivity, confidence, practice, and timing. If you are nervous, fearful, or aloof, then the trapping will be very rigid and stiff. I've seen people do 5 strikes in a blinding second, and it was incredible. I've personally sparred with some Muay thai and MMA guys and I've gotten a chance to smack them around many times. They always try to clinch or attempt to take me down, because they don't know wtf is going on when they getting smacked around in that close range. The thing about trapping is, it works, but watch out for the take down and clinch, because if you don't effectively defend or attack, then they will get you. If you get them good before they can clinch of take you down, then they have to back off and can't get you until the next time you close the gap and engage.
Many JKD guys say trapping doesn't work and it's because they simply haven't had enough intentional training and application of it... many just go back to the basics which is punching and kicking, which isn't bad, but don't talk shit about something that you don't even train and take seriously to begin with.