I have for years taught my pupils, group members when packing their machine away to put an odd piece of fabric in their machine, with the needle down, why? It stops dust and particles going down into the bobbin area and protects the needle are just a couple of reasons.
On buying my little Frister Rossman Cub 5 I found another reason, and what a discovery. When packed away without the fabric, for a considerable time look a the damage that occurred, fortunately I had a spare sewing plate from a recent machine.
When at first I looked at it closely I could actually see the shape of a presser foot on it, since then a few more bits of chrome have fallen off. I will be keeping it to show my pupils tha value of that little piece of fabric!