I used to be one of the "use it all up before buying new" types of people. But then I decided that life it too short to deal with thread that shreds or tangles, or with a rotary blade that doesn't cut. OR any other tool that isn't right for the job. Men always have to have just the right tool for their hobbies, so why not women?? So I now make sure I have the right tool for the job, wether it's the right kind of thread, a new blade for my cutter (after all you don't see men trying to cut wood with a dull saw), or a new ruler to make measuring and cutting fabric easier.
So, if I get a spool of thread that I don't want to use for sewing, it either gets thrown out, or depending on the type of thread, used to make "thread fabric". (This is usually made with embroidery thread ends, placed between two sheets of wash away stablilzer and sewn to keep all the thread "together"). This thread fabric can be used for all kinds of things, from pockets, to collars and cuff, or anything you want to add a fun and different look to.
I also bought a ton of rotary blades some time ago, when JoAnns had their quilting notions on sale for half price. I hadn't heard about the Harbor Freight idea at the time, and I had extra money then, so I may never have to buy another blade again... LOL