Not always, often tails you loose. Tail speak largely; they tell you how a dog is feeling. Whether it is happy, tense, scared or aggitated a tail says alot. Here is a great site to visit about tail positions.
I had the chance to listen in on a Sue Sternberg seminar years ago. One thing that stuck in my head was the circle tail. The circle tail is a very good tail, happy and very friendly. The dog actually wags their tail in a circle. My boy Luke does circle tail alot.
Yes the tail communicates alot but you must look at the rest of the body to see what is going on fully. Ears, body, eyes, mouth and tail; it's all a matter of communication for our canines.