I change my needle with every quilt and it also depends on how heavy the quilting is I will change it 3-4 times for one quilt.
Needles are cheap and I don't want and runs in the fabric with a dull needle.
I have the 8 thread Babylock Serger and love it.
I had an Elna however it was a pain to thread. My Babylock is the jetair self threader,what a blessing.
I use in eall the time for garm:)ents and finishing a rolled hem on tableclothes and baby blankets.