All it is is a history of all the connections it's blocked/allowed. It's totally useless. To get rid of it (assuming you're using PeerGuardian2), open up PeerGuardian and click on 'View History'. Then click file, then click 'Clear Database'. Just do this one every couple of months to keep it a small file. Just deleted mine which was at 115MB. Also, under the 'Settings' tab of the main program, uncheck 'Log Allowed Connections' under the History heading, and that should keep the file smaller too.
Just look at the amount of connections it blocks when you start downloading a torrent or connect ot a P2P network. For me, it blocks 1000s a day, from companies like Time-Warner, Sony, AOL, etc. So I guess it must be pretty good.