In another thread I mentioned that my B17 was sagging quite a bit even after tensioning. I decided to take some members' advice and lace it up. I didn't have a leather punch so I used a power drill. It worked well but didn't make as clean a hole as I'm sure a punch would. I used some nylon laces I had lying around. I drilled the holes in relation to the Brooks insignias on the sides then found out that one is further forward than the other. It's slightly asymmetrical but not bad.
First thing I noticed when I took it for a spin was that it was very firm again and it felt like my saddle had been raised about 1/4 inch (due to the lack of sag). It also felt slightly narrower due to the sides being pulled in. I'm really liking it. The vast majority of my weight is supported on my sit-bones again and I can lean forward without getting pressure in the middle parts. I highly recommend trying this if your leather saddle is getting too loose on you.