Rayon is thought to be weaker than cotton or poly threads, which makes sense because it's "digested and reconstituted" cellulose (I actually made it in high school organic chemistry). The fibers have been weakened as part of the process of creating it.
It has a reputation for not being colorfast - fading and/or bleeding when machine washed.
It would likely be fine for decorative use like a wall hanging (be careful pressing, and don't use steam), but I wouldn't use rayon thread for any project that might need to be cleaned or washed outside of dusting/soft-brush vacuuming.