I, too , use up spools of thread, putting the last few yards of a spool on the bobbin. Much better to run out of thread in the bobbin than from the spool, which can cause some nasty thread nests. One time I thought I was going to have to take the machine in to the repair man, it was so tight.
I have read that years ago, quilts were pieced with white or black or red thread. I can't imagine the reason for the red, unless it is like Onebyone said, it makes you happy.