Bearded Iris: why I remove old leaves

I do have a bit of a "thing" about removing old leaves from Bearded Iris: this has always been for two reasons, but now it has gone up to three. As soon as a leaf goes yellow-ish, and droops, then it is no longer photosynthesising, and therefore of no particular use to the plant: it has done its duty, and is time to gracefully retire, not hang about going limp and mushy. Like these ones: these are…