[QUOTE=Macybaby;8521142]I'm another that saves my "left on bobbin" thread for piecing. My LA does not have a sensor, so it's usually only the very last bobbin I need to deal with. Since these are large bobbins, I rewind it to those for my main piecing machine and then use them when the color will work, though I never worry about a good match, mostly using dark on dark quilts and lights on light quilts.
When I have a bit of thread left on my long arm bobbin, I will leave it in the machine, and then when I load the next quilt, I use it to bast the batting to the backing, and finally the flimsy to the batting and backing. It usually is easy to see for removal and a lot of times I will just toss the rest left on the bobbin. If it runs out while doing the basting thing, I just put in the new bobbin for the backing. I do have extra long arm bobbins and will usually wind 3-5 depending on the size of the quilt and will save what is left of the most common colors I use. I haven't got into using the prewounds. I have only an "L" size bobbin on my long arm.