It is usually just a stressor, indicating what is to come is probably obvious with a little thought, but is an important point.
Over-used, it becomes a meaningless cliché of no more significance than any other speech place-holder, like "errr". Or worse, implying self-importance.
"Stressor". Is there such a word? I've heard of Tensors, but they are Something Very Mathematical, I am no mathematician and anyway stress can be tension, but they are not opposites!