I have a well established calla that does well left in the ground in Western NY. The heads have now become heavy, and I wonder if I should dead-head them or if the inside of the flower is a seed of some sort.
Do you know Jack-in-the Pulpit? It is in the same family as calla. The spadix, the upright form in the middle of the flower becomes a cluster of berries if it is pollinated. A cultivar may be sterile, the growers having sacrificed berries for the intriguing color. Anyway, I dead-head my calla. Like dead-heading other plants, this may divert plant energy from seed formation to making new flowers. And it is highly unlikely that you could grow new plants from calla seed and they would not look like the parent plant even if you could. I don't see any advantage to keeping the spent flower except to satisfy curiosity.