I’m guessing here, but upvotes and downvotes are still useful as a tool to sort the better replies from the shitty ones, but I don’t think Lemmy keeps track of your “karma” on your profile like reddit. Hopefully that will stop people from just posting bullshit to karma farm.

Bots farming karma for account resale. Constant reposting of any material that can yield some useless internet points made many communities infested with mediocrity and repetition.

I wouldn’t say they’re “huge” issues, but I didn’t like the system because it made cases like these happen:

• People with big karma numbers (100k or more) that only posted shitposts and/or reposts, and people wanting to buy these accounts just for a bit of funny internet points.
• New users having to comment on subreddits they’re not interested in due to minimum karma requirements, which may increase lurkers. I understand they were trying to stop trolls and bots, but I’m not sure if this was the best solution.
• Some people simply downvote comments containing opinions that they don’t agree with, which are later collapsed by default for having low karma counts. This discourages potentially interesting discussions and punishes people for not agreeing with the majority of users in any sub, creating echo chambers.