Inevitably, BBSs accumulate messages which are useless, obsolete, or even intentionally obscene. You need to weed them from time to time, and this can take some time to do.
You should also check the messages for legal content. The jury is still out on whether a BBS Sysop can be held legally responsible for messages posted on his board (I don't think so, but I'm not the "judge").
And if you're trying to run a BBS with a particular purpose or style, you'll want to push it in the right direction and filter out unwanted diversions.