The benefits from following a troll are the sheer entertainment value of watching a mentally unhinged human being post rambling meaningless content in your steemit feed. Or source material for a great doctoral dissertation. Either case works.
Most trolls aren't intellectual enough to post content and will just resteem content from their fellow steemit kindred spirits such as DTube videos about Alex Jones.
Following and unfollowing a troll is simple. Just go to the troll's steemit profile. Find the either very low or negative reputation number and look to the right of that number and there will be either a follow or unfollow box. Clicking on that button icon will change it from one to the other.
There's not much you can do about the voting power of a troll but from what I can tell more than 90% of trolls will have extremely weak voting power along with a small reputation number so the trolls really can't meaningfully affect the posts of legitimate steemit users.
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