Any "treatments" for leaf spot needs to be done, before you ever have leaf spot ! For general iris health, you need "uncrowded" plants...so they get air and sun, a "clean slate", in the previous year...all the trash, dead leaves, stalks, etc., removed , and "trashed' (not composted). The "fungal spores" that actually cause the fungal type of leaf spot are 'everywhere', so, if the amount in the beds can be reduced...you will have less leaf spot...solarization works, as do fungicides (if you aren't against using "chemicals"')...fungicides need to be applied, starting when "new growth" begins, and continued throughout the growing season...a spray every 10days-2 weeks, depending on rainfall amounts...it also helps to "switch off" fungicides, as the spores will become "immune", if the same chemical is always used.
That said...you are still going to have leaf spot ! Hopefully, not much, and not everywhere in the bed, but, when the humidity sets in
As to trimming the leaves, for better appearance , yeah, it makes them look better....if there isn't a BIG problem...if there is, well, irises don't "look right" with only one, or two, stubby leaves ! And, when you are "in the beds", trimming spotted leaves, you are dropping spores from those "trimmings", or brushing against the "spots" on one plant, and depositing them on another. Your pets can be "culprits" in this, as well. And, IMHO, even a "badly spotted" leaf....say only 50% green, supplies 50% more "ooomph" to the plant than NO leaf does, so I don't remove any leaves, until they are "spent".
Some cultivars are more prone to leaf spot, than others, and SIB's, and Spuria irises seem pretty well immune to it, so , that could be an option, too.
One thing, the "treatment" for fungal leaf spot prevention (clean beds, air flow, sun exposure, etc.)also are big helps for the prevention of the bacterial form of leaf spot, and both fungal, and bacterial rot.