I will take the time to view the pins being shared as I want my pins to be shared with an audience who resonates with my products. I also check to see how active the board is. I belong to several group boards and once I started updating my boards, I realized one that a few have changed directions or were not meeting my needs. You have to stay on top of the content being shared.
Group Board i don't prefer any more . I used to have one recipe related Group board and it had around 15K follows.
I got feed-up cleaning all spam and irreverent pins . Also Pinterest warned me about this . But at the end , I endup deleting the board completely.
Point is , if any group board has good amount of follows , then only irreverent pin and spam you will find . Also i believe Pinterest also take action and any pin published there will not reach all the member afterwards. So all your effect will be lost.
I have found some boards to join because of Facebook groups focused on Pinterest or Etsy sellers. If you search in Facebook "Pinterest Group Board" you'll find a bunch and see what group seems like a good fit.
I also do Tailwind Tribes and have success with it.
I also started my own Facebook group just for Etsy/Pinterest users in my state. We are only at 89 members but it's good group who actually engage with each other.