I'd say banning own posts/comments would be preferable to deleting them on any count (for normal users, if they were given this power for own contributions): posts become inaccessible, so that further discussion is stopped, and any item can be easily un-banned, while deleted posts/comments can't be undeleted.

As a moderator, you can't ban users, only individual contributions, so if you ban some of your own comments, your don't ban your whole account.