1. Having a home page field - most forums don't need it at all and it's primarily used by spammers.
2. The members list - similar to the above, but I can't think of any real reason for having it.
Can anyone else think of anything that XF has built in that is more of a legacy than a real feature that forum admins and members really need? I can say for 100% that the two I mentioned, I wouldn't miss if they were gone and they're just headaches to have.