Don't know if modern computerized machines are more finicky, but in prehistoric times, when I was growing up, we only had like 3 bobbins. We always were winding on top of existing thread and it worked just fine. Also, we had 1 needle size & type and only changed it if it broke. You can always just put it on the thread spindle & use it for the top thread for piecing if you want to run it out.