I wrap the thread around an old shop plastic loyalty card and use the thread for basting usually for English Paper Piecing. When it gets too big, then I throw the extra thread away.
When I lived in a house that had an woodburning stove I would put cotton threads and cotton scraps (ONLY COTTONS) into an old saucepan with candle nubbins or the bits of wax from scented jar candles, melt them all together, poured the mixture out in an old cookie pan and once cooled break or cut it up into pieces to use as firelighters. Made the room smell lovely.
Some of the members in our quilt group save thread, tiny scraps and cuttings for a charity that sells it all on to a company that pulps and shreds it down for commercial and industrial uses.
HettyB