I cut mine back this year. Man do my iris beds look neat and tidy. Last year a had a slight rot problem and a huge ink spot problem. I hope that have all of that extra foliage off will keep the ink spot at bay!
As for the tree leaves...I have left them in the past and have discovered wonderful new growth under them in the spring. However, last year it took me a bit too long to get them all off and I was breaking off bloom stalks as I was trying to get the thick, wet layer of leaves off of the plants. It was a mess that I hope to avoid by having shorter foliage this year. Shorter foliage should give me less leaves (in theory anyway).
Before I "thought" I knew anything about irises, I would mow them off with the lawn mower when they were done blooming. I didn't know better and didn't like the mess they left behind so...off with their heads!!! I did not ever notice a decrease in bloom and they didn't die so.....
