Text is good to stimulate imagination. But sometimes, or should I say, most of the time, our imagination is very different from the reality. We tend to see a perfect view of what we focus on, and when reallity hits, we are disappointed. That's one of the reason why webcam came into place. People wanted to see each other experience instant emotions, versus waiting for the oher to type the whole sentence, somewhat killing the emotion itself. Those webcams originated from video conferencing needs, then it democratized itself pretty well to reach a very decent price. Now you can get a webcam for as low as 10$. Though te quality will not be on par of the most expensive models, still it gives you a start.
Sometimes you want to build some effects, or create a scenario, and some element, like thoughts, can't be expressed visually or verbally, they have to be typed. That's why most of those webcam chat programs include a place where you can actually type text. This allow you to add some more background to your interaction, side notes, reminders, etc ... Text include the use of shortcuts or smileys. And those are used in such specific context that a couple characters, usually less than 4, mean a lot ! That really adds up to the atmosphere of the discussion.
So now you know what to do, try it, experience it, and make your own opinion about webcam chat. See you there ;)