I planted a patch of iris bulbs last autumn which have really flowered well but do I have to remove the dead flowers?
I always do, it saves them trying to make seed.
Yup - spent flowers will waste the plant's energy as it will want to form seedheads, so removing the heads encourages the plant to keep making flowers. Keeps them looking tidy too.
Were they the dwarf kind that flower in late winter/early spring or the dutch Iris that flower just now barry? Leave all the foliage to die down before removing and if they're in pots you can just put them aside somewhere quiet till next year. If they're in borders or beds just remove the foliage once it's all died back. It feeds the bulbs for the following year.