As long as I am sewing, ironing, cutting, etc. and need my sewing machine, I leave it on, just like I leave my iron on when I'm piecing. I have an auto shutoff on my iron, so even if I forget to unplug it for a bit, the light will flash and let me know it's on when I've left the room. I usually don't turn my sewing machine off until I'm done for the day. Knock on wood, so far I have only had to replace the light bulb on my Janome 4000 once in over 15+ years