One of my quilting themed t-shirts is "It's all fun and games until the bobbin runs out".
As part of my vision issues, I can't really see the stitches as they come out of the back of the machine, and just did one of those long side seams where I got done but had run out of thread after about the first 4 inches. Also, I pin a lot and that also helps hide that the two pieces aren't sewn together.
I do like prewound bobbins, my friend's long arm couldn't wind a decent bobbin and not only did the prewounds work better but they also lasted longer.
I haven't done any of my tests lately, with hand sewing I've done a number of tests about the grain/direction of the threads, particularly with cotton and cotton wrapped threads. For that I've learned that yes, some threads are very fussy on direction and which way you take them off the spool. But we don't always know ultimately which that direction is. I don't know if it is just a perception bias, but I do know I seem to have more problems with black/dark thread and have been told that it is because it is often from redyed stock and has been wound back and forth multiple times. Can't think of a single time I've had major issues with a white/neutral thread. Anyway, I have learned that some times it is the thread's fault and some spools are not worth my time and energy.
Now that I'm using a poly thread (So Fine) I may have different results. Maybe I'll try running some bobbins and using them on the top.