The cut-a-way on knits keep the design from stretching and breaking the threads.
GREAT question...and as usual, the cuties have wonderful answers! I love learning from you guys! :-)
It is what is cheapest and easiest to get. Cutaway has been around a very long time and is used on most anything.
I have noticed on many embroidered items that are bought retail that they use only cut-away stabilizers. I am not so handy with a scissors, I have knicked the fabric of more than my fair share of projects cutting out the stabilizer so I only use tear away and wss now.
I use the scissors with the round ends, that way I only cut the stabilizer not the fabric!