Such an interesting subject. I think most of us use our needles until our sewing starts changing, i.e. skipped stitches, frayed thread, etc. I always change when something is not "normal". I always change when going from sewing to embroidery. My problem is changing to the "right size" needle. If there is an 90 in it, it is a 80 I use. I have recieved free needles with orders from Nancy's notions - Klase. These I do not like. I used 3 in 2 days making a small wall hanging.