Different subreddits had different rules. In some subs you needed loads of karma to post.

Karma farming was also used to bump up the account so that it could be sold to malicious buyers for propaganda or spam posting purposes.

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.