Yes, it is safe to delete the file if you don't need the info yourself as it has been already mentioned.

You can't turn it off but you could set up a scheduled task for deleting it periodically. How this is done depends on your OS. In my Fedora Core 6 Linux I've put a simple delete script under /etc/cron.weekly/ which cleans up all kinds of stuff including the render log. If you're on windows you can use the task scheduler or whatever it's called (can't remember).