To be honest there are still some boards I have never visited so far, like: Meetups, Press, Goods, Ivory Tower and a few more for sure. I don't think there is much knowledge I can acquire from these particular boards.
I would not say that it is necessary to visit each board, but sometimes people focus only on few boards and completely ignore the rest of the forum. Some even put specific boards on ignore, mostly because they consider them as
only spam boards. But if you for instance ignore
Bitcoin Discussion, you will ignore
Important Announcements, and some users would probably save their coins if they read that child board (Electrum phishing warning).
My advice was mostly focused on new users who join this forum only for bounty, and then spend 99% time in those boards, then after month or two complain how it is impossible to get merits on this forum. This is the wrong approach that has very little benefit for the user, but also for the forum in general.