If I am sewing a lot, I tend to change my needles more often, as I can keep track of how much I have been sewing, and I probably change it every 6-8 hours of sewing. If I only have time to sew here and there, I lose track of how long I have had a needle in, and I know I have gone longer than 8 hours with a needle. Not a real problem, as long as you don't have any problems with your stitches. But if you hear any thumping noise, see skipped stitches,"runs" in your fabric it definitely is time to do a change of your needle.