If it's a new saddle, don't tighten it until you absolutely have to. I put a half turn on my first Brooks B17 about 5 years after I bought it. Once you reach the end of that bolt, it's a new saddle.
second hand saddle, but doesn't look much used (but I don't know that). it had been slackened all the way to the end of the bolt (ie, no threads showing at the nose of the saddle), or I guess never tightened. It was beyond feeling like a slack hammock... I tightened it up a little, so now around 1 cm of threads showing at the front. Feels much better, very comfy on long days. It's my first Brook's, and the previous owner threw it in with the bike as he hated the saddle. Maybe I'm just very heavy