What kind of irises are you growing, if not bearded?
If they were bearded, I would say to: pull or trim off the dead leaves. If the leaf tips are brown or diseased, you can carefully cut back to the green part. (You should probably disinfect your pruners between cuts.)
In general (regardless what type of iris), this is spring time, the plants are actively growing, why rob them of their food (from photosynthesis) by cutting the foliage back? (The only good reason is for disease control, only if there is disease present, and only cutting out the diseased parts.)
Jmho, I'm sure the experts will weigh in.
