It can also be used for a pause, usually a longer one than a comma. When reading out a line, you would give a comma a very short pause, maybe enough for a short breath, but an ellipsis would indicate a far more noticeable one like you might find in an extremely awkward conversation or when a speaker is slowing down as if they see something coming at them in the middle of a sentence and they gradually stop talking as the 'oh shit' realization takes over.
Example, let's use the world of Jurassic Park for this, a group is roaming the island and one of them is talking, then suddenly a large carnivorous species of dinosaur pops its head up and the speaker slowly begins to finish his sentence or stop entirely. In text, this would be shown through ellipsis. When used at the end of a sentence, yes, it does indicate an omission, but it indicates a more drastic pause than a comma when in the middle of the sentence.