I use the same bobbin until ALL thread is gone if project not finished
embroidering before I just change bobbin and keep going.
However since I do TONS of FSL I have bobbins with the same color
of thread as I use with the top. I keep them in bobbin boxes and put
a 1/2" dot sticker with the color # so I can match the same color as
before.
I don't waste ANY bobbin thread and ALL embroidery thread tails that
is cut off goes into a special storage box with locking lid to be used in
a art project someday.