"I completely agree, and i think everybody understands that eventually using it will be mandatory. But for me the true question is rather when would be the right time to switch? When you start learning, it's just impossible. But a bit even later, suppose you are reading a easy book or a manga, if you need 20 min for every word you didn't understand, it harms your reading flow in a bad way. I think that you should use a monolingual dictionary either when you have the time "to go on discovery" or a good enough already that it won't take you significantly longer than looking at a En-Jp one. Also your vocabulary should be large enough to have some significant gain from it." - benjamin claverie