I guess I am compulsive too. When I purchased my Bernina my dealer emphasized the importance of cleaning and oiling every 3 bobbin fulls. So I only load 3 bobbins at a time. When I have used up my 3rd bobbin I stop and clean out the lint and give her a few drops of oil in the bobbin race. Needles I am not so good at. I change them for thread types or when I hit a pin and break them. The only other time I remember to change out a dull needle is if I am working with batiks. A dull needle makes a very distinct "popping" noise on batiks. So I will change out when I hear that noise.