Its taken me a few years of riding Brooks saddles to to finally figure them out. You need to really watch out for when they start to sag. It may feel super comfortable, but it throws out your fit leading to saddle sores and numbness from sliding around and being supported not by your sit bones, but by softer areas. After tensioning my B17 last summer I needed to lower my seatpost about 1 cm to compensate.

On that same saddle I probably used far too much proofide and the sides would flare out while riding. It appeared that no amount of tensioning would fix that, so I laced it instead.

My first Brooks was a pre-aged B17 which came laced. The laces can also help cut down on squeaking by limiting the vertical movement of the saddle leather.