I use a universal 80/12 for the majority of my tasks (piecing cottons, quilting with 50wt thread). I do change needles if the situation calls for it ... heavier weight thread (30wt and lower) and metallic thread are just two examples of when I change the needle. You should also change to a different type of needle (ball point) for certain applications like jersey knits, and use a microtex for fabrics like silks and lame.