Hi,
My machine has just about every bell and whistle and it's hard to pick the favorite....but.....I'd say my bobbin is running out of thread signal and the automatic pressure foot setting - it goes up when you stop sewing and goes back down when you start...for appliqueing it is fantastic! You can rotate your piece around all those little edges and not have to use one hand for the pressure foot...also can set it to lock your stitches at the start for you and cut it at the end.
Bev