Keep your site privacy *and* automatic pingbacks!
Pingbacks are automatic notifications added (as a kind of comment) to posts you link to in your articles. Whether a visitor is reading something way back in your archives or your most recent post, the pingbacks makes sure she can easily find any follow ups.
This is great for keeping related articles together, but private blogs are forced to disable Pingbacks to avoid notifying other sites when linking to them!
"Only Self Pings" solves this by only allowing pings to your own site (and whatever URLs you add to the whitelist).