SandyGirl ... in speaking of your threads being expensive or not. Do check the number of yards vs. cost. At first I totally hesitated on the Aurifil, then I realized that because of the finer thread, the yardage was a lot more on what appeared to be the same size spool ........... and I soon got rid of any guilt in it being my thread of choice for piecing. Sometimes, I even use it for quilting too.
ManiacQuilter2 ... Bernina sets their machines up with Mettler Silk Finished Threads (at least the newer ones) and thus why they recommend such. Not that you can't use others, just that the tension may need to be adjusted to meet the thread. Because Aurifil is my most highly used thread, the techie always sets my machine for Aurifil ... and I make the adjustments when using others. (I just need to remember to remind him!)