Tencel is a cellulose fiber similar to rayon, viscose and modal. It has wonderful drape and is supposed to be a good fabric for travel clothes because its not supposed to hold wrinkles for long. I have used Cascades Pima/Tencel to make crocheted summer hats and I would use and it is suggested to use it for form fitted summer tops like White Lies Design's Shapely Tank. I would also knit flowing skirts or sweaters with it. As far as stretchiness, I think it would depend on the yarn's constuction in addition to the fabric construction. The Pima/Tencel is a fully blended worsted weight and is not stretchy but the hats I've made with it are a bit and hold their shape better than plain cotton would. A cabled or knitted tube yarn might be stretchier.
I often go to the manufacturer or distributor websites and read what they say about the yarn and look at any patterns they offer for the yarn. That usually gives me a good idea if I can't see the yarn in person. Sometimes looking at yarns with the same fiber content on different websites will give you a better idea of how to use it.
I hope this helps.