I change my needle after every project when I clean out the bobbin case and all it’s parts. More often if I am using a fabric like flannel, fleece or something like that. I try to be vigilant about that!

I change needles every project. More often if I need to.

I only change my needle when I break one or when I hear a "popping" noise as if it is having a hard time going thru the fabrics.

Or if i forget to change the plate out and try to zig with a single hole plate!

When I start a new project

Yes! It's happened to me too :)

Yeah, the plate issue... I'm usually caught by not having changed my 1/4" foot. That's such a terrible sound!

My rule is: Every new full sized quilt deserves a new needle.

I clean my machine after every project or every 2 weeks. I never thought to change needles - I do that when the sound changes. I have a computer vacuum that has a 1.4 inch nozzle attachment to clean way down under.

I change my needle if it sounds 'off', catches in the fabric because of a burr or bend or it breaks. I never sew over pins. I use the right size and type of needle for the project that I am working on. I have started using the titanium needles and they last a very long time. I can't imagine changing needles every project or every eight hours.