Leaves can act as insulation. But I usually clear them out of the beds because we get a lot of rain over the winter months and the leaves trap too much moisture.
As for cutting fans. I cut back the Japanese iris because they produce a thick clump and it's better to cut them back than leave them to become home for mice and insects. The bearded iris I will cut back when it gets really cold, about December. The Louisiana's I leave alone because this is their growing period.
