The purpose for cutting the leaves is because the plants have not firmly rooted themselves in place and will continue to flop over until new roots have established. It is also to prevent further transpiration from occurring until there are new roots to compensate for the moisture loss. The Rhizomes will not produce new leaf growth until it has enough roots to support the moisture needs of a growing leaf. I am assuming the recommendation to not cut the leaves is based upon an assumption that these leaves are still performing some kind of photo-synthesis, however nearly all of the plant's attention is being diverted to root production. There is little to zero photo-synthesis occurring in these desiccated leaves. Rhizomes are essentially starch (stored energy), they contain enough nutrients to re-grow leaves, but do not contain enough moisture to support matured leaves in the absence of established roots. This is why the leaves flopped and look horrendous. These leaves are dying and will be replaced. Not cutting the leaves back serves only to pose a disease risk due to their weakened state and continuous contact with the soil which I assume is being kept moist.

These are bearded irises, they actively grow for 6-8 weeks after blooming (Late May through July in Virginia), and continue to perform photosynthesis throughout the remainder of the summer and early fall. They do not have a summer "rest" period like some of the bulbous iris or desert iris species. This is why the ideal transplant time for bearded Iris is August through October depending on how early frost typically arrives. This allows the plants to grow and recover from the exhausting task of blooming, while providing time for new roots to establish before winter. I know some in the southwest recommend spring transplanting despite the depletion caused by blossoming. This is because the summers in the southwest are so brutal the plants won't survive a late summer or early fall transplant due to the sustained heat and dehydration. In Virginia the ideal time to transplant and divide is early September.

Recommendations from Schreiner's Iris Gardens:

https://www.schreinersgardens.com/dividing-and-transplanting-bearded-iris 

Cheers,

Werner