Rule 5. Locking.

This is for Lemmy, not PieFed. Banned users can be completely wiped, removing all content (including from the modlog). This is helpful for CSAM accounts. They can also just be banned from an instance, or a community, with all content remaining up thus far. Users that are instance-banned are invisible to users from that instance, but often can actually comment on that instance from the perspective of their home instance.

As an example, if someone permabanned me from Lemmy.world, Lemmy.world users could not ever see my comments, even the ones only on Lemmy.ml. However, Lemmy.ml users would be able to see my comments on Lemmy.world posts, and I would still be able to comment. I'd effectively be user-defederated.

There's more to it than that, it's actually kinda complicated. PieFed works differently too.

When a moderator bans someone they have the choice to remove that person's posts and comments too

In the communities I moderate I usually leave comments intact unless they are offensive, I'm happy enough to let people see me trying to reason with the person and then being unreasonable before banning them

You can often still see the person's deleted comment or post of you look at their profile

I don't think a banned person can vote on a community, as we banned serial down voters from one community the down votes reduced

Or maybe some instance doesn't delete.