I do it in specific instances where I want to express a pause, like "that was....ok?" I also use it when I want what I'm saying to come off as annoyed. "The shipment was late, again..."
I actually worry about exclamation points because I use them like OPs image, but I always worry people take it as yelling or something lol
I think they have attention span problems or something like that. They can't wait while they are forming sentences, so while they think of something, they add ellipses to their message.