Mass taggers have historically been abused to ban or shadow-ban users who've posted in "bad" subreddits.
If you argued with someone in r/the Donald, you'd magically be unable to participate in a large swath of unrelated communities. Trying to appeal the bans would often result in you being permanently muted or receiving a snarky response from the mods saying it's your fault for engaging in said 'bad' communities.
There were some grassroots efforts around 2015 to make the mod log public and transparent (so it'd say what was removed, by who, and optionally why), but it was unfortunately opt-in and never gained large adoption.