Right now I'm using up all the threads that came when my mother came to live with me. Using up all the lightest colors first and moving on to the darker shades when working on a dark quilt. Of course if the thread is on a wood spools I just toss it as I'm sure its too old and will break or at least I'm thinking it will. I was shocked when I noticed how high the price of thread has gotten in recent years so when I find a good sale on white or light colored all purpose threads I stock up. If I can find it in the cone size, more the better. Its amazing how much thread we go thru in putting a quilt together.
I'm also using some quilting thread that came with my quilt machine as it seems it doesn't like it so why waste it. I'm sure it would work now that I've gotten used to the machine and know how to adjust the tension but just never got around to it plus "pink" is not my color and have yet to quilt a top needing pink thread.