Yesterday, I was looking at the iceberg roses in my son's garden which were full of blooms and I was explaining to him that he should remove the dead heads in order to promote more roses.
Many people do not know this and it applies to most plants.
When the faded blooms are removed, you are telling the plant to make more.
If the faded blooms are left on the plants, - then the plant puts its energy into making seed as opposed to flowers. - In other words, once there is nothing left but dead flower heads, these will become seeds and no more blooms will appear.
In a nut shell, the plant has finished its cycle for the season.
Obviously, the plant will eventually stop making more blooms despite dead heading as it also knows that the season has come to an end, but one can push just a little further and have a slightly longer season with regular dead heading.