As soon as the flowers fade the flower stalks should be cut short.As long as there are seeds forming on your plant the nurishment is going to the seed.
Bill

I have not experienced any problems from leaving the berries on the plant. All my plants that are vigorous seem to produce flowers every year even with the seeds still in place. (I generally leave the seed pods on the plant for at least 10 months.)

On the other hand, I believe it is a bad idea to cut the flower stalk (or scape). It can rot back into the heart of the plant if you do that. If you don't want to produce seeds, pull the seed pods off but leave the scape to dry up to the point where you can pull it out from the base. This can take up to two months. This is common advice on the Clivia Enthusiast list serve.