I know you can't post in certain subreddits without some amount of Karma but it is usually low like 10 or something.
So I don't know why you would really care about an account with thousands of karma.
I don't think Karma plays a role in post viability or anything like that but I could be wrong.
In reddit mostly porn bots were karma farmers they spammed on certain subs where they got lots of likes and probably later on got into a scam or spam bot that tried to make money.
Funny thing is on r/worldpolitics you could post without any karma and no mods were present but bot attacks got downvoted very hard. Like politics or anything that the people didn't like there.