Found a few things:
This link is to a clear and informative article about left and right twist:
http://www.funfun-japan.com/index.php?S%20or%20Z%3F
This is a quote from another article:
'Thread is twisted to the left or twisted to the right, depending on its use. Left-twist thread is always used in the sewing machine because the action of the stitch-forming mechanism tends to ravel or break right-twist thread. Left- or right- twist thread may be used for hand sewing. The terms that designate left-twist threads are machine, machine twist, left twist, and Z twist. A cord or thread has left (or Z) twist if, when held in a vertical position, the twist of the yarn follows the slope of the central portion of the letter Z'
Looks like worst case scenario is if you use right twist thread in a sewing machine, it will likely break or ravel.
Hope this helps. I learned plenty LOL!