My Japanese is good enough that I can understand shows pretty well without subs unless there's tons of technical jargon, so for me there's not much point in watching dubs, especially since you inevitably lose some subtext in translation. I have nothing against them in principle, but the only time I watch them is for nostalgia purposes with shows I watched as a small child or when watching with friends and family who prefer dubs. They're also an accessibility aid for those with visual and learning disabilities (I know someone with dyslexia who struggles mightily with subs).

Even for other languages, though, I always prefer hearing the original language over a dub. There are plenty of talented dub actors out there, but I'd rather hear the original performance that fit the director's vision unconstrained by artificial lip flap or timing requirements. Also, if I'm watching foreign media I want to be immersed in that cultural context, which language is a huge part of.